summaryrefslogtreecommitdiff
path: root/Master/texmf-dist/source/latex/l3packages/xparse/xparse.dtx
blob: 1a2e9767429d92e21edd7717f546f79a2d9e2a9b (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
3079
3080
3081
3082
3083
3084
3085
3086
3087
3088
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
3147
3148
3149
3150
3151
3152
3153
3154
3155
3156
3157
3158
3159
3160
3161
3162
3163
3164
3165
3166
3167
3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
3180
3181
3182
3183
3184
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194
3195
3196
3197
3198
3199
3200
3201
3202
3203
3204
3205
3206
3207
3208
3209
3210
3211
3212
3213
3214
3215
3216
3217
3218
3219
3220
3221
3222
3223
3224
3225
3226
3227
3228
3229
3230
3231
3232
3233
3234
3235
3236
3237
3238
3239
3240
3241
3242
3243
3244
3245
3246
3247
3248
3249
3250
3251
3252
3253
3254
3255
3256
3257
3258
3259
3260
3261
3262
3263
3264
3265
3266
3267
3268
3269
3270
3271
3272
3273
3274
3275
3276
3277
3278
3279
3280
3281
3282
3283
3284
3285
3286
3287
3288
3289
3290
3291
3292
3293
3294
3295
3296
3297
3298
3299
3300
3301
3302
3303
3304
3305
3306
3307
3308
3309
3310
3311
3312
3313
3314
3315
3316
3317
3318
3319
3320
3321
3322
3323
3324
3325
3326
3327
3328
3329
3330
3331
3332
3333
3334
3335
3336
3337
3338
3339
3340
3341
3342
3343
3344
3345
3346
3347
3348
3349
3350
3351
3352
3353
3354
3355
3356
3357
3358
3359
3360
3361
3362
3363
3364
3365
3366
3367
3368
3369
3370
3371
3372
3373
3374
3375
3376
3377
3378
3379
3380
3381
3382
3383
3384
3385
3386
3387
3388
3389
3390
3391
3392
3393
3394
3395
3396
3397
3398
3399
3400
3401
3402
3403
3404
3405
3406
3407
3408
3409
3410
3411
3412
3413
3414
3415
3416
3417
3418
3419
3420
3421
3422
3423
3424
3425
3426
3427
3428
3429
3430
3431
3432
3433
3434
3435
3436
3437
3438
3439
3440
3441
3442
3443
3444
3445
3446
3447
3448
3449
3450
3451
3452
3453
3454
3455
3456
3457
3458
3459
3460
3461
3462
3463
3464
3465
3466
3467
3468
3469
3470
3471
3472
3473
3474
3475
3476
3477
3478
3479
3480
3481
3482
3483
3484
3485
3486
3487
3488
3489
3490
3491
3492
3493
3494
3495
3496
3497
3498
3499
3500
3501
3502
3503
3504
3505
3506
3507
3508
3509
3510
3511
3512
3513
3514
3515
3516
3517
3518
3519
3520
3521
3522
3523
3524
3525
3526
3527
3528
3529
3530
3531
3532
3533
3534
3535
3536
3537
3538
3539
3540
3541
3542
3543
3544
3545
3546
3547
3548
3549
3550
3551
3552
3553
3554
3555
3556
3557
3558
3559
3560
3561
3562
3563
3564
3565
3566
3567
3568
3569
3570
3571
3572
3573
3574
3575
3576
3577
3578
3579
3580
3581
3582
3583
3584
3585
3586
3587
3588
3589
3590
3591
3592
3593
3594
3595
3596
3597
3598
3599
3600
3601
3602
3603
3604
3605
3606
3607
3608
3609
3610
3611
3612
3613
3614
3615
3616
3617
3618
3619
3620
3621
3622
3623
3624
3625
3626
3627
3628
3629
3630
3631
3632
3633
3634
3635
3636
3637
3638
3639
3640
3641
3642
3643
3644
3645
3646
3647
3648
3649
3650
3651
3652
3653
3654
3655
3656
3657
3658
3659
3660
3661
3662
3663
3664
3665
3666
3667
3668
3669
3670
3671
3672
3673
3674
3675
3676
3677
3678
3679
3680
3681
3682
3683
3684
3685
3686
3687
3688
3689
3690
3691
3692
3693
3694
3695
3696
3697
3698
3699
3700
3701
3702
3703
3704
3705
3706
3707
3708
3709
3710
3711
3712
3713
3714
3715
3716
3717
3718
3719
3720
3721
3722
3723
3724
3725
3726
3727
3728
3729
3730
3731
3732
3733
3734
3735
3736
3737
3738
3739
% \iffalse meta-comment
%
%% File: xparse.dtx (C) Copyright 1999 Frank Mittelbach, Chris Rowley,
%%                      David Carlisle
%%                  (C) Copyright 2004-2008 Frank Mittelbach,
%%                      The LaTeX3 Project
%%                  (C) Copyright 2009-2016 The LaTeX3 Project
%%
%% It may be distributed and/or modified under the conditions of the
%% LaTeX Project Public License (LPPL), either version 1.3c of this
%% license or (at your option) any later version.  The latest version
%% of this license is in the file
%%
%%    http://www.latex-project.org/lppl.txt
%%
%% This file is part of the "l3packages bundle" (The Work in LPPL)
%% and all files in that bundle must be distributed together.
%%
%% The released version of this bundle is available from CTAN.
%%
%% -----------------------------------------------------------------------
%%
%% The development version of the bundle can be found at
%%
%%    http://www.latex-project.org/svnroot/experimental/trunk/
%%
%% for those people who are interested.
%%
%%%%%%%%%%%
%% NOTE: %%
%%%%%%%%%%%
%%
%%   Snapshots taken from the repository represent work in progress and may
%%   not work or may contain conflicting material!  We therefore ask
%%   people _not_ to put them into distributions, archives, etc. without
%%   prior consultation with the LaTeX Project Team.
%%
%% -----------------------------------------------------------------------
%%
%
%<*driver|package>
% The version of expl3 required is tested as early as possible, as
% some really old versions do not define \ProvidesExplPackage.
\RequirePackage{expl3}[2016/05/14]
%<package>\@ifpackagelater{expl3}{2016/05/14}
%<package>  {}
%<package>  {%
%<package>    \PackageError{xparse}{Support package l3kernel too old}
%<package>      {%
%<package>        Please install an up to date version of l3kernel\MessageBreak
%<package>        using your TeX package manager or from CTAN.\MessageBreak
%<package>        \MessageBreak
%<package>        Loading xparse will abort!%
%<package>      }%
%<package>    \endinput
%<package>  }
\def\ExplFileName{xparse}
\def\ExplFileDescription{L3 Experimental document command parser}
\def\ExplFileDate{2016/05/14}
\def\ExplFileVersion{6495}
%</driver|package>
%<*driver>
\documentclass[full]{l3doc}
\usepackage{amstext}
\begin{document}
  \DocInput{\jobname.dtx}
\end{document}
%</driver>
% \fi
%
% \providecommand\acro[1]{\textsc{\MakeLowercase{#1}}}
% \newenvironment{arg-description}{%
%   \begin{itemize}\def\makelabel##1{\hss\llap{\bfseries##1}}}{\end{itemize}}
%
% \title{^^A
%   The \textsf{xparse} package\\ Document command parser^^A
%   \thanks{This file describes v\ExplFileVersion,
%     last revised \ExplFileDate.}^^A
% }
%
% \author{^^A
%  The \LaTeX3 Project\thanks
%    {^^A
%      E-mail:
%        \href{mailto:latex-team@latex-project.org}
%          {latex-team@latex-project.org}^^A
%    }^^A
% }
%
% \date{Released \ExplFileDate}
%
% \maketitle
%
% \begin{documentation}
%
% The \pkg{xparse} package provides a high-level interface for
% producing document-level commands. In that way, it is intended as
% a replacement for the \LaTeXe{} \cs{newcommand} macro. However,
% \pkg{xparse} works so that the interface to a function (optional
% arguments, stars and mandatory arguments, for example) is separate
% from the internal implementation. \pkg{xparse} provides a normalised
% input for the internal form of a function, independent of the
% document-level argument arrangement.
%
% At present, the functions in \pkg{xparse} which are regarded as
% \enquote{stable} are:
% \begin{itemize}
%   \item \cs{DeclareDocumentCommand}
%   \item \cs{NewDocumentCommand}
%   \item \cs{RenewDocumentCommand}
%   \item \cs{ProvideDocumentCommand}
%   \item \cs{DeclareDocumentEnvironment}
%   \item \cs{NewDocumentEnvironment}
%   \item \cs{RenewDocumentEnvironment}
%   \item \cs{ProvideDocumentEnvironment}
%   \item \cs{DeclareExpandableDocumentCommand}
%   \item \cs{IfNoValue(TF)}
%   \item \cs{IfBoolean(TF)}
% \end{itemize}
% with the other functions currently regarded as \enquote{experimental}. Please
% try all of the commands provided here, but be aware that the
% experimental ones may change or disappear.
%
% \subsection{Specifying arguments}
%
% Before introducing the functions used to create document commands,
% the method for specifying arguments with \pkg{xparse} will be
% illustrated. In order to allow each argument to be defined
% independently, \pkg{xparse} does not simply need to know the
% number of arguments for a function, but also the nature of each
% one. This is done by constructing an \emph{argument specification},
% which defines the number of arguments, the type of each argument
% and any additional information needed for \pkg{xparse} to read the
% user input and properly pass it through to internal functions.
%
% The basic form of the argument specifier is a list of letters, where
% each letter defines a type of argument. As will be described below,
% some of the types need additional information, such as default values.
% The argument types can be divided into two, those which define
% arguments that are mandatory (potentially raising an error if not
% found) and those which define optional arguments. The mandatory types
% are:
% \begin{itemize}[font=\ttfamily]
%   \item[m] A standard mandatory argument, which can either be a single
%     token alone or multiple tokens surrounded by curly braces.
%     Regardless of the input, the argument will be passed to the
%     internal code surrounded by a brace pair. This is the \pkg{xparse}
%     type specifier for a normal \TeX{} argument.
%   \item[l] An argument which reads everything up to the first
%     open group token: in standard \LaTeX{} this is a left brace.
%   \item[r] Reads a \enquote{required} delimited argument, where the
%     delimiters are given as \meta{token1} and \meta{token2}:
%     \texttt{r}\meta{token1}\meta{token2}. If the opening \meta{token}
%     is missing, the default marker |-NoValue-| will be inserted after
%     a suitable error.
%   \item[R] As for \texttt{r}, this is a \enquote{required} delimited
%     argument but has a user-definable recovery \meta{default}, given
%     as \texttt{R}\meta{token1}\meta{token2}\marg{default}.
%   \item[u] Reads an argument \enquote{until} \meta{tokens} are encountered,
%     where the desired \meta{tokens} are given as an argument to the
%     specifier: \texttt{u}\marg{tokens}.
%   \item[v] Reads an argument \enquote{verbatim}, between the following
%     character and its next occurrence, in a way similar to the argument
%     of the \LaTeXe{} command \cs{verb}. Thus a \texttt{v}-type argument
%     is read between two matching tokens, which cannot be any of |%|, |\|,
%     |#|, |{|, |}| or \verb*| |.
%     The verbatim argument can also be enclosed between braces, |{| and |}|.
%     A command with a verbatim
%     argument will not work when it appears within an argument of
%     another function.
% \end{itemize}
% The types which define optional arguments are:
% \begin{itemize}[font=\ttfamily]
%   \item[o] A standard \LaTeX{} optional argument, surrounded with square
%     brackets, which will supply
%     the special |-NoValue-| marker if not given (as described later).
%   \item[d] An optional argument which is delimited by \meta{token1}
%     and \meta{token2}, which are given as arguments:
%     \texttt{d}\meta{token1}\meta{token2}. As with \texttt{o}, if no
%     value is given the special marker |-NoValue-| is returned.
%   \item[O] As for \texttt{o}, but returns \meta{default} if no
%     value is given.  Should be given as \texttt{O}\marg{default}.
%   \item[D] As for \texttt{d}, but returns \meta{default} if no
%     value is given: \texttt{D}\meta{token1}\meta{token2}\marg{default}.
%     Internally, the \texttt{o}, \texttt{d} and \texttt{O} types are
%     short-cuts to an appropriated-constructed \texttt{D} type argument.
%   \item[s] An optional star, which will result in a value
%     \cs{BooleanTrue} if a star is present and \cs{BooleanFalse}
%     otherwise (as described later).
%   \item[t] An optional \meta{token}, which will result in a value
%     \cs{BooleanTrue} if \meta{token} is present and \cs{BooleanFalse}
%     otherwise. Given as \texttt{t}\meta{token}.
%   \item[g] An optional argument given inside a pair of \TeX{} group
%     tokens (in standard \LaTeX, |{| \ldots |}|), which returns
%     |-NoValue-| if not present.
%   \item[G] As for \texttt{g} but returns \meta{default} if no value
%     is given: \texttt{G}\marg{default}.
%   \item[k] An optional \emph{key} argument which requires a \emph{value}:
%     the key should be a single \meta{token}. If the key is not present,
%     returns |-NoValue-|. \emph{This is an experimental type}.
%   \item[K] As for \texttt{K} but returns \meta{default} if no value
%     is given: \texttt{K}\meta{token}\marg{default}.
%     \emph{This is an experimental type}.
% \end{itemize}
%
% Using these specifiers, it is possible to create complex input syntax
% very easily. For example, given the argument definition
% `|s o o m O{default}|', the input `|*[Foo]{Bar}|' would be parsed as:
% \begin{itemize}[nolistsep]
%   \item |#1| = |\BooleanTrue|
%   \item |#2| = |Foo|
%   \item |#3| = |-NoValue-|
%   \item |#4| = |Bar|
%   \item |#5| = |default|
% \end{itemize}
% whereas `|[One][Two]{}[Three]|' would be parsed as:
% \begin{itemize}[nolistsep]
%   \item |#1| = |\BooleanFalse|
%   \item |#2| = |One|
%   \item |#3| = |Two|
%   \item |#4| = ||
%   \item |#5| = |Three|
% \end{itemize}
%
% Delimited argument types (\texttt{d}, \texttt{o} and \texttt{r}) are
% defined such that they require matched pairs of delimiters when collecting
% an argument. For example
% \begin{verbatim}
%   \DeclareDocumentCommand{\foo}{o}{#1}
%   \foo[[content]] % #1 = "[content]"
%   \foo[[]         % Error: missing closing "]"
% \end{verbatim}
% Also note that |{| and |}| cannot be used as delimiters as they are used
% by \TeX{} as grouping tokens. Arguments to be grabbed inside these tokens
% must be created as either \texttt{m}- or \texttt{g}-type arguments.
%
% Within delimited arguments, non-balanced or otherwise awkward tokens may
% be included by protecting the entire argument with a brace pair
% \begin{verbatim}
%   \DeclareDocumentCommand{\foo}{o}{#1}
%   \foo[{[}]         % Allowed as the "[" is 'hidden'
% \end{verbatim}
% These braces will be stripped if they surround the \emph{entire} content
% of the optional argument
% \begin{verbatim}
%   \DeclareDocumentCommand{\foo}{o}{#1}
%   \foo[{abc}]         % => "abc"
%   \foo[ {abc}]         % => " {abc}"
% \end{verbatim}
%
% Two more tokens have a special meaning when creating an argument
% specifier. First, \texttt{+} is used to make an argument long (to
% accept paragraph tokens). In contrast to \LaTeXe's \cs{newcommand},
% this applies on an argument-by-argument basis. So modifying the
% example to `|s o o +m O{default}|' means that the mandatory argument
% is now \cs{long}, whereas the optional arguments are not.
%
% Secondly, the token \texttt{>} is used to declare so-called
% \enquote{argument processors}, which can be used to modify the contents of an
% argument before it is passed to the macro definition. The use of
% argument processors is a somewhat advanced topic, (or at least a less
% commonly used feature) and is covered in Section~\ref{sec:processors}.
%
% By default, an argument of type~\texttt{v} must be at most one line.
% Prefixing with \texttt{+} allows line breaks within the argument.  The
% argument is given as a string of characters with category codes~$12$
% or~$13$, except spaces, which have category code~$10$.
%
% \subsection{Spacing and optional arguments}
%
% \TeX{} will find the first argument after a function name irrespective
% of any intervening spaces. This is true for both mandatory and
% optional arguments. So |\foo[arg]| and \verb*|\foo   [arg]| are
% equivalent. Spaces are also ignored when collecting arguments up
% to the last mandatory argument to be collected (as it must exist).
% So after
% \begin{verbatim}
%   \DeclareDocumentCommand \foo { m o m } { ... }
% \end{verbatim}
% the user input |\foo{arg1}[arg2]{arg3}| and
% \verb*|\foo{arg1}  [arg2]   {arg3}| will both be parsed in the same
% way. However, spaces are \emph{not} ignored when parsing optional
% arguments after the last mandatory argument. Thus with
% \begin{verbatim}
%   \DeclareDocumentCommand \foo { m o } { ... }
% \end{verbatim}
% |\foo{arg1}[arg2]| will find an optional argument but
% \verb*|\foo{arg1} [arg2]| will not. This is so that trailing optional
% arguments are not picked up \enquote{by accident} in input.
%
% There is one major exception to the rules listed above: when
% \pkg{xparse} is used to define what \TeX\ defines as \enquote{control
% symbols} in which the function name is made up of a single character,
% such as \enquote{\cmd{\\}}, spaces are \emph{not} ignored directly
% after them even for mandatory arguments.
%
% \subsection{Required delimited arguments}
%
% The contrast between a delimited (\texttt{D}-type) and \enquote{required
% delimited} (\texttt{R}-type) argument is that an error will be raised if
% the latter is missing. Thus for example
% \begin{verbatim}
%   \DeclareDocumentCommand\foo{r()m}
%   \foo{oops}
% \end{verbatim}
% will lead to an error message being issued. The marker |-NoValue-|
% (\texttt{r}-type) or user-specified default (for \texttt{R}-type) will be
% inserted to allow error recovery.
%
% Users should note that support for required delimited arguments is somewhat
% experimental. Feedback is therefore very welcome on the \texttt{LaTeX-L}
% mailing list.
%
% \subsection{Verbatim arguments}
%
% Arguments of type~\texttt{v} are read in verbatim mode, which will
% result in the grabbed argument consisting of tokens of category codes
% $12$~(\enquote{other}) and $13$~(\enquote{active}), except spaces,
% which are given category code $10$~(\enquote{space}). The argument is
% delimited in a similar manner to the \LaTeXe{} \cs{verb} function.
%
% Functions containing verbatim arguments cannot appear in the arguments
% of other functions. The \texttt{v}~argument specifier includes code to check
% this, and will raise an error if the grabbed argument has already been
% tokenized by \TeX{} in an irreversible way.
%
% Users should note that support for verbatim arguments is somewhat
% experimental. Feedback is therefore very welcome on the \texttt{LaTeX-L}
% mailing list.
%
% \subsection{Declaring commands and environments}
%
% With the concept of an argument specifier defined, it is now
% possible to describe the methods available for creating both
% functions and environments using \pkg{xparse}.
%
% The interface-building commands are the preferred method for
% creating document-level functions in \LaTeX3. All of the functions
% generated in this way are naturally robust (using the \eTeX{}
% \cs{protected} mechanism).
%
% \begin{function}
%   {
%     \DeclareDocumentCommand ,
%     \NewDocumentCommand     ,
%     \RenewDocumentCommand   ,
%     \ProvideDocumentCommand
%   }
%   \begin{syntax}
%     \cs{DeclareDocumentCommand} \meta{Function} \Arg{arg spec} \Arg{code}
%   \end{syntax}
%   This family of commands are used to create a document-level
%   \meta{function}. The argument specification for the function is
%   given by \meta{arg spec},  and expanding
%   to be replaced by the \meta{code}.
% \end{function}
%
%   As an example:
%   \begin{verbatim}
%     \DeclareDocumentCommand \chapter { s o m }
%       {
%         \IfBooleanTF {#1}
%           { \typesetstarchapter {#3} }
%           { \typesetnormalchapter {#2} {#3} }
%       }
%   \end{verbatim}
%   would be a way to define a \cs{chapter} command which would
%   essentially behave like the current \LaTeXe{} command (except that it
%   would accept an optional argument even when a \texttt{*} was parsed).
%   The \cs{typesetnormalchapter} could test its first argument for being
%   |-NoValue-| to see if an optional argument was present.
%
%   The difference between the \cs{Declare\ldots}, \cs{New\ldots}
%   \cs{Renew\ldots} and \cs{Provide\ldots} versions is the behaviour
%   if \meta{function} is already defined.
%   \begin{itemize}
%     \item \cs{DeclareDocumentCommand} will always create the new
%       definition, irrespective of any existing \meta{function} with the
%       same name.
%    \item \cs{NewDocumentCommand} will issue an error if \meta{function}
%      has already been defined.
%    \item \cs{RenewDocumentCommand} will issue an error if \meta{function}
%      has not previously been defined.
%    \item \cs{ProvideDocumentCommand} creates a new definition for
%      \meta{function} only if one has not already been given.
%   \end{itemize}
%
%   \begin{texnote}
%      Unlike \LaTeXe{}'s \cs{newcommand} and relatives, the
%      \cs{DeclareDocumentCommand} family of functions do not prevent creation of
%      functions with names starting \cs{end\ldots}.
%   \end{texnote}
%
% \begin{function}
%   {
%     \DeclareDocumentEnvironment ,
%     \NewDocumentEnvironment     ,
%     \RenewDocumentEnvironment   ,
%     \ProvideDocumentEnvironment
%   }
%   \begin{syntax}
%     \cs{DeclareDocumentEnvironment} \Arg{environment} \Arg{arg spec}
%     ~~\Arg{start code} \Arg{end code}
%   \end{syntax}
%   These commands work in the same way as \cs{DeclareDocumentCommand},
%   etc., but create environments (\cs{begin}|{|\meta{function}|}| \ldots
%   \cs{end}|{|\meta{function}|}|). Both the \meta{start code} and
%   \meta{end code}
%   may access the arguments as defined by \meta{arg spec}.
% \end{function}
%
% \subsection{Testing special values}
%
% Optional arguments created using \pkg{xparse} make use of dedicated
% variables to return information about the nature of the argument
% received.
%
% \begin{function}[EXP,TF]{\IfNoValue}
%   \begin{syntax}
%     \cs{IfNoValueTF} \Arg{argument} \Arg{true code} \Arg{false code}
%     \cs{IfNoValueT} \Arg{argument} \Arg{true code}
%     \cs{IfNoValueF} \Arg{argument} \Arg{false code}
%   \end{syntax}
%   The \cs{IfNoValue(TF)} tests are used to check if \meta{argument} (|#1|,
%   |#2|, \emph{etc.}) is the special |-NoValue-| marker For example
%   \begin{verbatim}
%     \DeclareDocumentCommand \foo { o m }
%       {
%         \IfNoValueTF {#1}
%           { \DoSomethingJustWithMandatoryArgument {#2} }
%           {  \DoSomethingWithBothArguments {#1} {#2}   }
%       }
%   \end{verbatim}
%   will use a different internal function if the optional argument
%   is given than if it is not present.
%
%   Note that three tests are available, depending on which outcome
%   branches are required: \cs{IfNoValueTF}, \cs{IfNoValueT} and
%   \cs{IfNoValueF}.
%
%   As the \cs{IfNoValue(TF)} tests are expandable, it is possible to
%   test these values later, for example at the point of typesetting or
%   in an expansion context.
%
%   It is important to note that |-NoValue-| is constructed such that it
%   will \emph{not} match the simple text input |-NoValue-|, \emph{i.e.}
%   that
%   \begin{verbatim}
%     \IfNoValueTF{-NoValue-}
%   \end{verbatim}
%   will be logically \texttt{false}.
% \end{function}
%
% \begin{function}[EXP,TF]{\IfValue}
%   \begin{syntax}
%     \cs{IfValueTF} \Arg{argument} \Arg{true code} \Arg{false code}
%    \end{syntax}
%   The reverse form of the \cs{IfNoValue(TF)} tests are also available
%   as \cs{IfValue(TF)}. The context will determine which logical
%   form makes the most sense for a given code scenario.
% \end{function}
%
% \begin{variable}{\BooleanFalse, \BooleanTrue}
%   The \texttt{true} and \texttt{false} flags set when searching for
%   an optional token (using \texttt{s} or \texttt{t\meta{token}}) have
%   names which are accessible outside of code blocks.
% \end{variable}
%
% \begin{function}[EXP,TF]{\IfBoolean}
%   \begin{syntax}
%     \cs{IfBooleanTF} \meta{argument} \Arg{true code} \Arg{false code}
%   \end{syntax}
%   Used to test if \meta{argument} (|#1|, |#2|, \emph{etc.}) is
%   \cs{BooleanTrue} or \cs{BooleanFalse}. For example
%   \begin{verbatim}
%     \DeclareDocumentCommand \foo { s m }
%       {
%         \IfBooleanTF #1
%           { \DoSomethingWithStar {#2} }
%           { \DoSomethingWithoutStar {#2} }
%       }
%   \end{verbatim}
%   checks for a star as the first argument, then chooses the action to
%   take based on this information.
% \end{function}
%
% \subsection{Argument processors}
% \label{sec:processors}
%
% \pkg{xparse} introduces the idea of an argument processor, which is
% applied to an argument \emph{after} it has been grabbed by the
% underlying system but before it is passed to \meta{code}. An argument
% processor can therefore be used to regularise input at an early stage,
% allowing the internal functions to be completely independent of input
% form. Processors are applied to user input and to default values for
% optional arguments, but \emph{not} to the special \cs{NoValue} marker.
%
% Each argument processor is specified by the syntax
% \texttt{>}\marg{processor} in the argument specification. Processors
% are applied from right to left, so that
% \begin{verbatim}
%   >{\ProcessorB} >{\ProcessorA} m
% \end{verbatim}
% would apply \cs{ProcessorA}
% followed by \cs{ProcessorB} to the tokens grabbed by the \texttt{m}
% argument.
%
% \begin{variable}{\ProcessedArgument}
%   \pkg{xparse} defines a very small set of processor functions. In the
%   main, it is anticipated that code writers will want to create their
%   own processors. These need to accept one argument, which is the
%   tokens as grabbed (or as returned by a previous processor function).
%   Processor functions should return the processed argument as the
%   variable \cs{ProcessedArgument}.
% \end{variable}
%
% \begin{function}{\ReverseBoolean}
%   \begin{syntax}
%     \cs{ReverseBoolean}
%   \end{syntax}
%   This processor reverses the logic of \cs{BooleanTrue} and
%   \cs{BooleanFalse}, so that the example from earlier would become
%   \begin{verbatim}
%     \DeclareDocumentCommand \foo { > { \ReverseBoolean } s m }
%       {
%         \IfBooleanTF #1
%           { \DoSomethingWithoutStar {#2} }
%           { \DoSomethingWithStar {#2} }
%       }
%   \end{verbatim}
% \end{function}
%
% \begin{function}[updated = 2012-02-12]{\SplitArgument}
%   \begin{syntax}
%     \cs{SplitArgument} \Arg{number} \Arg{token}
%   \end{syntax}
%   This processor splits the argument given at each occurrence of the
%   \meta{token} up to a maximum of \meta{number} tokens (thus
%   dividing the input into $\text{\meta{number}} + 1$ parts).
%   An error is given if too many \meta{tokens} are present in the
%   input. The processed input is placed inside
%   $\text{\meta{number}} + 1$ sets of braces for further use.
%   If there are fewer than \Arg{number} of \Arg{tokens} in the argument
%   then \cs{NoValue} markers are added at the end of the processed
%   argument.
%   \begin{verbatim}
%     \DeclareDocumentCommand \foo
%       { > { \SplitArgument { 2 } { ; } } m }
%       { \InternalFunctionOfThreeArguments #1 }
%   \end{verbatim}
%   Any category code $13$ (active) \meta{tokens} will be replaced
%   before the split takes place. Spaces are trimmed at each end of each
%   item parsed.
% \end{function}
%
% \begin{function}{\SplitList}
%   \begin{syntax}
%     \cs{SplitList} \Arg{token(s)}
%   \end{syntax}
%   This processor splits the argument given at each occurrence of the
%   \meta{token(s)} where the number of items is not fixed. Each item is
%   then wrapped in braces within |#1|. The result is that the
%   processed argument can be further processed using a mapping function.
%   \begin{verbatim}
%     \DeclareDocumentCommand \foo
%       { > { \SplitList { ; } } m }
%       { \MappingFunction #1 }
%   \end{verbatim}
%   If only a single \meta{token} is used for the split, any
%   category code $13$ (active) \meta{token} will be replaced
%   before the split takes place.
% \end{function}
%
% \begin{function}[EXP]{\ProcessList}
%   \begin{syntax}
%     \cs{ProcessList} \Arg{list} \Arg{function}
%   \end{syntax}
%   To support \cs{SplitList}, the function \cs{ProcessList} is available
%   to apply a \meta{function} to every entry in a \meta{list}. The
%   \meta{function} should absorb one argument: the list entry. For example
%   \begin{verbatim}
%     \DeclareDocumentCommand \foo
%       { > { \SplitList { ; } } m }
%       { \ProcessList {#1} { \SomeDocumentFunction } }
%   \end{verbatim}
%
%   \textbf{This function is experimental.}
% \end{function}
%
% \begin{function}{\TrimSpaces}
%   \begin{syntax}
%     \cs{TrimSpaces}
%   \end{syntax}
%   Removes any leading and trailing spaces (tokens with character code~$32$
%   and category code~$10$) for the ends of the argument. Thus for example
%   declaring a function
%   \begin{verbatim}
%     \DeclareDocumentCommand \foo
%       { > { \TrimSpaces } m }
%       { \showtokens {#1} }
%   \end{verbatim}
%   and using it in a document as
%   \begin{verbatim}
%     \foo{ hello world }
%   \end{verbatim}
%   will show \texttt{hello world} at the terminal, with the space at each
%   end removed. \cs{TrimSpaces} will remove multiple spaces from the ends of
%   the input in cases where these have been included such that the standard
%   \TeX{} conversion of multiple spaces to a single space does not apply.
%
%   \textbf{This function is experimental.}
% \end{function}
%
% \subsection{Fully-expandable document commands}
%
% There are \emph{very rare} occasion when it may be useful to create
% functions using a fully-expandable argument grabber. To support this,
% \pkg{xparse} can create expandable functions as well as the usual
% robust ones. This imposes a number of restrictions on the nature of
% the arguments accepted by a function, and the code it implements.
% This facility should only be used when \emph{absolutely necessary};
% if you do not understand when this might be, \emph{do not use these
% functions}!
%
% \begin{function}{\DeclareExpandableDocumentCommand}
%   \begin{syntax}
%     \cs{DeclareExpandableDocumentCommand}
%     ~~~~\meta{function} \Arg{arg spec} \Arg{code}
%   \end{syntax}
%   This command is used to create a document-level \meta{function},
%   which will grab its arguments in a fully-expandable manner. The
%   argument specification for the function is given by \meta{arg spec},
%   and the function will execute \meta{code}. In  general, \meta{code} will
%   also be fully expandable, although it is possible that this will
%   not be the case (for example, a function for use in a table might
%   expand so that \cs{omit} is the first non-expandable token).
%
%   Parsing arguments expandably imposes a number of restrictions on
%   both the type of arguments that can be read and the error checking
%   available:
%   \begin{itemize}
%     \item The last argument (if any are present) must be one of the
%       mandatory types \texttt{m} or \texttt{r}.
%     \item All arguments are either short or long: it is not possible
%       to mix short and long argument types.
%     \item The mandatory argument types \texttt{l} and \texttt{u} are
%       not available.
%     \item The \enquote{optional group} argument types \texttt{g} and
%       \texttt{G} are not available.
%     \item The \enquote{verbatim} argument type \texttt{v} is not available.
%     \item Argument processors (using \texttt{>}) are not available.
%     \item It is not possible to differentiate between, for example
%       |\foo[| and |\foo{[}|: in both cases the \texttt{[} will be
%       interpreted as the start of an optional argument. As a
%       result, checking for optional arguments is less robust than
%       in the standard version.
%   \end{itemize}
%   \pkg{xparse} will issue an error if an argument specifier is given
%   which does not conform to the first six requirements. The last
%   item is an issue when the function is used, and so is beyond the
%   scope of \pkg{xparse} itself.
% \end{function}
%
% \subsection{Access to the argument specification}
%
% The argument specifications for document commands and environments are
% available for examination and use.
%
% \begin{function}{\GetDocumentCommandArgSpec, \GetDocumentEnvironmentArgSpec}
%   \begin{syntax}
%     \cs{GetDocumentCommandArgSpec} \meta{function}
%     \cs{GetDocumentEnvironmentArgSpec} \meta{environment}
%   \end{syntax}
%   These functions transfer the current argument specification for the
%   requested \meta{function} or \meta{environment} into the token list
%   variable \cs{ArgumentSpecification}. If the \meta{function} or
%   \meta{environment} has no known argument specification then an error
%   is issued. The assignment to \cs{ArgumentSpecification} is local to
%   the current \TeX{} group.
% \end{function}
%
% \begin{function}
%   {\ShowDocumentCommandArgSpec,  \ShowDocumentEnvironmentArgSpec}
%   \begin{syntax}
%     \cs{ShowDocumentCommandArgSpec} \meta{function}
%     \cs{ShowDocumentEnvironmentArgSpec} \meta{environment}
%   \end{syntax}
%   These functions show the current argument specification for the
%   requested \meta{function} or \meta{environment} at the terminal. If
%   the \meta{function} or \meta{environment} has no known argument
%   specification then an error is issued.
% \end{function}
%
% \section{Load-time options}
%
% \DescribeOption{log-declarations}
% The package recognises the load-time option \texttt{log-declarations},
% which is a key--value option taking the value \texttt{true} and
% \texttt{false}. By default, the option is set to \texttt{true}, meaning
% that each command or environment declared is logged. By loading
% \pkg{xparse} using
% \begin{verbatim}
%   \usepackage[log-declarations=false]{xparse}
% \end{verbatim}
% this may be suppressed and no information messages are produced.
%
% \end{documentation}
%
% \begin{implementation}
%
% \section{\pkg{xparse} implementation}
%
%    \begin{macrocode}
%<*package>
%    \end{macrocode}
%
%    \begin{macrocode}
%<@@=xparse>
%    \end{macrocode}
%
%    \begin{macrocode}
\ProvidesExplPackage
  {\ExplFileName}{\ExplFileDate}{\ExplFileVersion}{\ExplFileDescription}
%    \end{macrocode}
%
% \subsection{Variables and constants}
%
% \begin{variable}{\c_@@_no_value_tl}
%   A special \enquote{awkward} token list: it contains two |-|~tokens with
%   different category codes. This is used as the marker for nothing being
%   returned when no optional argument is given.
%    \begin{macrocode}
\tl_const:Nx \c_@@_no_value_tl
  { \char_generate:nn { `\- } { 11 } NoValue- }
%    \end{macrocode}
% \end{variable}
%
% \begin{variable}{\c_@@_shorthands_prop}
%   Shorthands are stored as a property list: this is set up here as it
%   is a constant.
%    \begin{macrocode}
\prop_new:N \c_@@_shorthands_prop
\prop_put:Nnn \c_@@_shorthands_prop { o } { d[] }
\prop_put:Nnn \c_@@_shorthands_prop { O } { D[] }
\prop_put:Nnn \c_@@_shorthands_prop { s } { t* }
%    \end{macrocode}
% \end{variable}
%
% \begin{variable}{\c_@@_special_chars_seq}
%   In \IniTeX{} mode, we store special characters in a sequence.
%   Maybe |$| or |&| will have to be added later.
%    \begin{macrocode}
%<*initex>
\seq_new:N \c_@@_special_chars_seq
\seq_set_split:Nnn \c_@@_special_chars_seq { }
  { \  \\ \{ \} \# \^ \_ \% \~ }
%</initex>
%    \end{macrocode}
% \end{variable}
%
% \begin{variable}{\l_@@_all_long_bool}
%   For expandable commands, all arguments have the same long status, but this
%   needs to be checked. A flag is therefore needed to track whether arguments
%   are long at all.
%    \begin{macrocode}
\bool_new:N \l_@@_all_long_bool
%    \end{macrocode}
% \end{variable}
%
% \begin{variable}{\l_@@_args_tl}
%   Token list variable for grabbed arguments.
%    \begin{macrocode}
\tl_new:N \l_@@_args_tl
%    \end{macrocode}
% \end{variable}
%
% \begin{variable}{\l_@@_command_arg_specs_prop}
%   Used to record all document commands created, and the argument
%   specifications that go with these.
%    \begin{macrocode}
\prop_new:N \l_@@_command_arg_specs_prop
%    \end{macrocode}
% \end{variable}
%
% \begin{variable}{\l_@@_current_arg_int}
%   The number of the current argument being set up: this is used for creating
%   the expandable auxiliary functions, and also to indicate if all arguments
%   are \texttt{m}-type.
%    \begin{macrocode}
\int_new:N \l_@@_current_arg_int
%    \end{macrocode}
% \end{variable}
%
% \begin{variable}{\l_@@_environment_bool}
%   Generating environments uses the same mechanism as generating functions.
%   However, full processing of arguments is always needed for environments,
%   and so the function-generating code needs to know this.
%    \begin{macrocode}
\bool_new:N \l_@@_environment_bool
%    \end{macrocode}
% \end{variable}
%
% \begin{variable}{\l_@@_environment_arg_specs_prop}
%   Used to record all document environment created, and the argument
%   specifications that go with these.
%    \begin{macrocode}
\prop_new:N \l_@@_environment_arg_specs_prop
%    \end{macrocode}
% \end{variable}
%
% \begin{variable}{\l_@@_expandable_bool}
%   Used to indicate if an expandable command is begin generated, as this
%   affects both the acceptable argument types and how they are implemented.
%    \begin{macrocode}
\bool_new:N \l_@@_expandable_bool
%    \end{macrocode}
% \end{variable}
%
% \begin{variable}{\l_@@_expandable_aux_name_tl}
%   Used to create pretty-printing names for the auxiliaries: although the
%   immediate definition does not vary, the full expansion does and so it
%   does not count as a constant.
%    \begin{macrocode}
\tl_new:N \l_@@_expandable_aux_name_tl
\tl_set:Nn \l_@@_expandable_aux_name_tl
  {
    \l_@@_function_tl \c_space_tl
    ( arg~ \int_use:N \l_@@_current_arg_int )
  }
%    \end{macrocode}
% \end{variable}
%
% \begin{variable}{\l_@@_fn_tl}
%   For passing the pre-formed name of the auxiliary to be used as the
%   parsing function.
%    \begin{macrocode}
\tl_new:N \l_@@_fn_tl
%    \end{macrocode}
% \end{variable}
%
% \begin{variable}{\l_@@_function_tl}
%   Holds the control sequence name of the function currently being
%   defined: used to avoid passing this as an argument and to avoid repeated
%   use of \cs{cs_to_str:N}.
%    \begin{macrocode}
\tl_new:N \l_@@_function_tl
%    \end{macrocode}
% \end{variable}
%
% \begin{variable}{\l_@@_long_bool}
%   Used to indicate that an argument is long: this is used on a per-argument
%   basis for non-expandable functions, or for the entire set of arguments
%   when working expandably.
%    \begin{macrocode}
\bool_new:N \l_@@_long_bool
%    \end{macrocode}
% \end{variable}
%
% \begin{variable}{\l_@@_m_args_int}
%   The number of \texttt{m} arguments: if this is the same as the total
%   number of arguments, then a short-cut can be taken in the creation of
%   the grabber code.
%    \begin{macrocode}
\int_new:N \l_@@_m_args_int
%    \end{macrocode}
% \end{variable}
%
% \begin{variable}{\l_@@_mandatory_args_int}
%   Holds the total number of mandatory arguments for a function, which is
%   needed to tell whether further mandatory arguments follow an optional
%   one.
%    \begin{macrocode}
\int_new:N \l_@@_mandatory_args_int
%    \end{macrocode}
% \end{variable}
%
% \begin{variable}{\l_@@_processor_bool}
%   Indicates that the current argument will be followed by one or more
%   processors.
%    \begin{macrocode}
\bool_new:N \l_@@_processor_bool
%    \end{macrocode}
% \end{variable}
%
% \begin{variable}{\l_@@_processor_int}
%   In the grabber routine, each processor is saved with a number
%   recording the order it was found in. The total is then used to work
%   back through the grabbers so they apply to the argument right to left.
%    \begin{macrocode}
\int_new:N \l_@@_processor_int
%    \end{macrocode}
% \end{variable}
%
% \begin{variable}{\l_@@_signature_tl}
%   Used when constructing the signature (code for argument grabbing) to
%   hold what will become the implementation of the main function.
%    \begin{macrocode}
\tl_new:N \l_@@_signature_tl
%    \end{macrocode}
% \end{variable}
%
% \begin{variable}{\l_@@_tmp_tl}
%   Scratch space.
%    \begin{macrocode}
\tl_new:N \l_@@_tmp_tl
%    \end{macrocode}
% \end{variable}
%
% \subsection{Declaring commands and environments}
%
% \begin{macro}{\@@_declare_cmd:Nnn, \@@_declare_expandable_cmd:Nnn}
% \begin{macro}[aux]{\@@_declare_cmd_aux:Nnn}
% \begin{macro}[int]
%   {\@@_declare_cmd_internal:Nnn, \@@_declare_cmd_internal:cnx}
%   The main functions for creating commands set the appropriate flag then
%   use the same internal code to do the definition.
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \@@_declare_cmd:Nnn
  {
    \bool_set_false:N \l_@@_expandable_bool
    \@@_declare_cmd_aux:Nnn
  }
\cs_new_protected_nopar:Npn \@@_declare_expandable_cmd:Nnn
  {
    \bool_set_true:N \l_@@_expandable_bool
    \@@_declare_cmd_aux:Nnn
  }
%    \end{macrocode}
%  The first stage is to log information, both for the user in the log and
%  for programmatic use in a property list of all declared commands.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_declare_cmd_aux:Nnn #1#2
  {
    \cs_if_exist:NTF #1
      {
        \__msg_kernel_info:nnxx { xparse } { redefine-command }
          { \token_to_str:N #1 } { \tl_to_str:n {#2} }
      }
      {
        \__msg_kernel_info:nnxx { xparse } { define-command }
          { \token_to_str:N #1 } { \tl_to_str:n {#2} }
      }
    \prop_put:Nnn \l_@@_command_arg_specs_prop {#1} {#2}
    \bool_set_false:N \l_@@_environment_bool
    \@@_declare_cmd_internal:Nnn #1 {#2}
  }
%    \end{macrocode}
%   The real business of defining a document command starts with setting up
%   the appropriate name, then counting up the number of mandatory arguments.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_declare_cmd_internal:Nnn #1#2#3
  {
    \tl_set:Nx \l_@@_function_tl { \cs_to_str:N #1 }
    \@@_count_mandatory:n {#2}
    \@@_prepare_signature:n {#2}
    \int_compare:nNnTF \l_@@_current_arg_int = \l_@@_m_args_int
      {
        \bool_if:NTF \l_@@_environment_bool
          { \@@_declare_cmd_mixed:Nn #1 {#3} }
          { \@@_declare_cmd_all_m:Nn #1 {#3} }
      }
      { \@@_declare_cmd_mixed:Nn #1 {#3} }
    \@@_break_point:n {#2}
  }
\cs_generate_variant:Nn \@@_declare_cmd_internal:Nnn { cnx }
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\@@_break_point:n}
%   A marker used to escape from creating a definition if necessary.
%    \begin{macrocode}
\cs_new_eq:NN \@@_break_point:n \use_none:n
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_declare_cmd_all_m:Nn, \@@_declare_cmd_mixed:Nn}
% \begin{macro}[aux]
%   {\@@_declare_cmd_mixed_aux:Nn, \@@_declare_cmd_mixed_expandable:Nn}
%   When all of the arguments to grab are simple \texttt{m}-type, a short
%   cut can be taken to provide only a single function. In the case of
%   expandable commands, this can also happen for \texttt{+m} (as all arguments
%   in this case must be long).
%    \begin{macrocode}
\cs_new_protected:Npn \@@_declare_cmd_all_m:Nn #1#2
  {
    \cs_generate_from_arg_count:Ncnn #1
      {
        cs_set
        \bool_if:NF \l_@@_expandable_bool { _protected }
        \bool_if:NF \l_@@_all_long_bool { _nopar }
        :Npn
      }
      \l_@@_current_arg_int {#2}
  }
%    \end{macrocode}
%   In the case of mixed arguments, any remaining \texttt{m}-type ones are
%   first added to the signature, then the appropriate auxiliary is called.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_declare_cmd_mixed:Nn
  {
    \bool_if:NTF \l_@@_expandable_bool
      { \@@_declare_cmd_mixed_expandable:Nn }
      { \@@_declare_cmd_mixed_aux:Nn }
   }
%    \end{macrocode}
%   Creating standard functions with mixed arg.~specs sets up the main function
%   to zero the number of processors, set the name of the function (for the
%   grabber) and clears the list of grabbed arguments.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_declare_cmd_mixed_aux:Nn #1#2
  {
    \@@_flush_m_args:
    \cs_generate_from_arg_count:cNnn
      { \l_@@_function_tl \c_space_tl code }
      \cs_set_protected:Npn \l_@@_current_arg_int {#2}
    \cs_set_protected_nopar:Npx #1
      {
        \int_zero:N \l_@@_processor_int
        \tl_set:Nn \exp_not:N \l_@@_args_tl
          { \exp_not:c { \l_@@_function_tl \c_space_tl code } }
        \tl_set:Nn \exp_not:N \l_@@_fn_tl
          { \exp_not:c { \l_@@_function_tl \c_space_tl } }
        \exp_not:o \l_@@_signature_tl
        \exp_not:N \l_@@_args_tl
      }
  }
\cs_new_protected:Npn \@@_declare_cmd_mixed_expandable:Nn #1#2
  {
    \cs_generate_from_arg_count:cNnn
      { \l_@@_function_tl \c_space_tl code }
      \cs_set:Npn \l_@@_current_arg_int {#2}
    \cs_set_nopar:Npx #1
      {
        \exp_not:o \l_@@_signature_tl
        \exp_not:N \@@_grab_expandable_end:wN
        \exp_not:c { \l_@@_function_tl \c_space_tl code }
        \exp_not:N \q_@@
        \exp_not:c { \l_@@_function_tl \c_space_tl }
      }
    \bool_if:NTF \l_@@_all_long_bool
      { \cs_set:cpx }
      { \cs_set_nopar:cpx }
      { \l_@@_function_tl \c_space_tl } ##1##2 { ##1 {##2} }
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\@@_declare_env:nnnn}
% \begin{macro}[int]{\@@_declare_env_internal:nnnn}
%   The lead-off to creating an environment is much the same as that for
%   creating a command: issue the appropriate message, store the argument
%   specification then hand off to an internal function.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_declare_env:nnnn #1#2
  {
%<*initex>
    \cs_if_exist:cTF { environment~ #1 }
%</initex>
%<*package>
    \cs_if_exist:cTF {#1}
%</package>
      {
        \__msg_kernel_info:nnxx { xparse } { redefine-environment }
          {#1} { \tl_to_str:n {#2} }
      }
      {
        \__msg_kernel_info:nnxx { xparse } { define-environment }
          {#1} { \tl_to_str:n {#2} }
      }
    \prop_put:Nnn \l_@@_environment_arg_specs_prop {#1} {#2}
    \bool_set_false:N \l_@@_expandable_bool
    \bool_set_true:N \l_@@_environment_bool
    \@@_declare_env_internal:nnnn {#1} {#2}
  }
%    \end{macrocode}
%   Creating a document environment requires a few more steps than creating
%   a single command. In order to pass the arguments of the command to the
%   end of the function, it is necessary to store the grabbed arguments.
%   To do that, the function used at the end of the environment has to be
%   redefined to contain the appropriate information. To minimize the amount
%   of expansion at point of use, the code here is expanded now as well as
%   when used.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_declare_env_internal:nnnn #1#2#3#4
  {
    \@@_declare_cmd_internal:cnx { environment~ #1 } {#2}
      {
        \cs_set_nopar:Npx \exp_not:c { environment~ #1 ~end~aux }
          {
            \exp_not:N \exp_not:N \exp_not:c { environment~ #1~end~aux~ }
            \exp_not:n { \tl_tail:N \l_@@_args_tl }
          }
        \exp_not:n {#3}
      }
    \cs_set_nopar:cpx { environment~ #1 ~end }
      { \exp_not:c { environment~ #1 ~end~aux } }
    \cs_generate_from_arg_count:cNnn
      { environment~ #1 ~end~aux~ } \cs_set:Npn
      \l_@@_current_arg_int {#4}
%<*package>
    \cs_set_eq:cc {#1}       { environment~ #1 }
    \cs_set_eq:cc { end #1 } { environment~ #1 ~end }
%</package>
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \subsection{Counting mandatory arguments}
%
% \begin{macro}{\@@_count_mandatory:n}
% \begin{macro}{\@@_count_mandatory:N}
% \begin{macro}[aux]{\@@_count_mandatory:N}
%   Loop through the signature to count up mandatory arguments before the
%   main parsing run. First, check if the current token is a short-cut for
%   another argument type. If it is, expand it and loop again. If not, then
%   look for a \enquote{counting} function to check the argument type. No error
%   is raised here if one is not found as one will be raised by later code.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_count_mandatory:n #1
  {
    \int_zero:N \l_@@_mandatory_args_int
    \@@_count_mandatory:N #1
      \q_recursion_tail \q_recursion_tail \q_recursion_tail \q_recursion_stop
  }
\cs_new_protected:Npn \@@_count_mandatory:N #1
  {
    \quark_if_recursion_tail_stop:N #1
    \prop_get:NnNTF \c_@@_shorthands_prop {#1} \l_@@_tmp_tl
      { \exp_after:wN \@@_count_mandatory:N \l_@@_tmp_tl }
      { \@@_count_mandatory_aux:N #1 }
  }
\cs_new_protected:Npn \@@_count_mandatory_aux:N #1
  {
    \cs_if_exist_use:cF { @@_count_type_ \token_to_str:N #1 :w }
      { \@@_count_type_m:w }
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}
%   {
%     \@@_count_type_>:w,
%     \@@_count_type_+:w,
%     \@@_count_type_d:w,
%     \@@_count_type_D:w,
%     \@@_count_type_g:w,
%     \@@_count_type_G:w,
%     \@@_count_type_k:w,
%     \@@_count_type_K:w,
%     \@@_count_type_m:w,
%     \@@_count_type_r:w,
%     \@@_count_type_R:w,
%     \@@_count_type_t:w,
%     \@@_count_type_u:w
%   }
%   For counting the mandatory arguments, a function is provided for each
%   argument type that will mop any extra arguments and call the loop function.
%   Only the counting functions for mandatory arguments actually do anything:
%   the rest are simply there to ensure the loop continues correctly. There are
%   no count functions for \texttt{l} or \texttt{v} argument types as they are
%   exactly the same as \texttt{m}, and so a little code can be saved.
%
%   The second thing that can be done here is to check that the signature is
%   actually valid, such that all of the various argument types have the
%   correct number of data items associated with them.  If this fails to be
%   the case, the entire set up is abandoned to avoid any strange internal
%   errors. The opportunity is also taken to make sure that where a single
%   token is required, one has actually been supplied.
%
%   The third is that processors and the marker~|+| for long arguments
%   must be followed by arguments.  For this, just check that the next
%   token is not \cs{q_recursion_tail}, and remember to leave it after
%   the looping macro.
%    \begin{macrocode}
\cs_new_protected:cpn { @@_count_type_>:w } #1#2
  {
    \quark_if_recursion_tail_stop_do:nn {#2} { \@@_bad_arg_spec:wn }
    \@@_count_mandatory:N #2
  }
\cs_new_protected:cpn { @@_count_type_+:w } #1
  {
    \quark_if_recursion_tail_stop_do:nn {#1} { \@@_bad_arg_spec:wn }
    \@@_count_mandatory:N #1
  }
\cs_new_protected:Npn \@@_count_type_d:w #1#2
  {
    \@@_single_token_check:n {#1}
    \@@_single_token_check:n {#2}
    \quark_if_recursion_tail_stop_do:Nn #2 { \@@_bad_arg_spec:wn }
    \@@_count_mandatory:N
  }
\cs_new_protected:Npn \@@_count_type_D:w #1#2#3
  {
    \@@_single_token_check:n {#1}
    \@@_single_token_check:n {#2}
    \quark_if_recursion_tail_stop_do:nn {#3} { \@@_bad_arg_spec:wn }
    \@@_count_mandatory:N
  }
\cs_new_protected_nopar:Npn \@@_count_type_g:w
  { \@@_count_mandatory:N }
\cs_new_protected:Npn \@@_count_type_G:w #1
  {
    \quark_if_recursion_tail_stop_do:nn {#1} { \@@_bad_arg_spec:wn }
    \@@_count_mandatory:N
  }
\cs_new_protected:Npn \@@_count_type_k:w #1
  {
    \@@_single_token_check:n {#1}
    \quark_if_recursion_tail_stop_do:Nn #1 { \@@_bad_arg_spec:wn }
    \@@_count_mandatory:N
  }
\cs_new_protected:Npn \@@_count_type_K:w #1#2
  {
    \@@_single_token_check:n {#1}
    \quark_if_recursion_tail_stop_do:nn {#2} { \@@_bad_arg_spec:wn }
    \@@_count_mandatory:N
  }
\cs_new_protected_nopar:Npn \@@_count_type_m:w
  {
    \int_incr:N \l_@@_mandatory_args_int
    \@@_count_mandatory:N
  }
\cs_new_protected:Npn \@@_count_type_r:w #1#2
  {
    \@@_single_token_check:n {#1}
    \@@_single_token_check:n {#2}
    \quark_if_recursion_tail_stop_do:Nn #2 { \@@_bad_arg_spec:wn }
    \int_incr:N \l_@@_mandatory_args_int
    \@@_count_mandatory:N
  }
\cs_new_protected:Npn \@@_count_type_R:w #1#2#3
  {
    \@@_single_token_check:n {#1}
    \@@_single_token_check:n {#2}
    \quark_if_recursion_tail_stop_do:nn {#3} { \@@_bad_arg_spec:wn }
    \int_incr:N \l_@@_mandatory_args_int
    \@@_count_mandatory:N
  }
\cs_new_protected:Npn \@@_count_type_t:w #1
  {
    \@@_single_token_check:n {#1}
    \quark_if_recursion_tail_stop_do:Nn #1 { \@@_bad_arg_spec:wn }
    \@@_count_mandatory:N
  }
\cs_new_protected:Npn \@@_count_type_u:w #1
  {
    \quark_if_recursion_tail_stop_do:nn {#1} { \@@_bad_arg_spec:wn }
    \int_incr:N \l_@@_mandatory_args_int
    \@@_count_mandatory:N
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_single_token_check:n}
% \begin{macro}[aux]{\@@_single_token_check_aux:nwn}
%   A spin-out function to check that what should be single tokens really
%   are single tokens.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_single_token_check:n #1
  {
    \exp_args:Nx \tl_if_single_token:nF { \tl_trim_spaces:n {#1} }
      { \@@_single_token_check_aux:nwn {#1} }
  }
\cs_new_protected:Npn \@@_single_token_check_aux:nwn
  #1#2 \@@_break_point:n #3
  {
    \__msg_kernel_error:nnx { xparse } { not-single-token }
      { \tl_to_str:n {#1} } { \tl_to_str:n {#3} }
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\@@_bad_arg_spec:wn}
%   If the signature is wrong, this provides an escape from the entire
%   definition process.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_bad_arg_spec:wn #1 \@@_break_point:n #2
  { \__msg_kernel_error:nnx { xparse } { bad-arg-spec } { \tl_to_str:n {#2} } }
%    \end{macrocode}
% \end{macro}
%
% \subsection{Preparing the signature: general mechanism}
%
% \begin{macro}{\@@_prepare_signature:n}
% \begin{macro}{\@@_prepare_signature:N}
% \begin{macro}{\@@_prepare_signature_bypass:N}
% \begin{macro}[aux]{\@@_prepare_signature_add:N}
%   Actually creating the signature uses the same loop approach as counting
%   up mandatory arguments. There are first a number of variables which need
%   to be set to track what is going on.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_prepare_signature:n #1
  {
    \bool_set_false:N \l_@@_all_long_bool
    \int_zero:N \l_@@_current_arg_int
    \bool_set_false:N \l_@@_long_bool
    \int_zero:N \l_@@_m_args_int
    \bool_set_false:N \l_@@_processor_bool
    \tl_clear:N \l_@@_signature_tl
    \@@_prepare_signature:N #1 \q_recursion_tail \q_recursion_stop
  }
%    \end{macrocode}
%  The main looping function does not take an argument, but carries out the
%  reset on the processor boolean. This is split off from the rest of the
%  process so that when actually setting up processors the flag-reset can
%  be bypassed.
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \@@_prepare_signature:N
  {
    \bool_set_false:N \l_@@_processor_bool
    \@@_prepare_signature_bypass:N
  }
\cs_new_protected:Npn \@@_prepare_signature_bypass:N #1
  {
    \quark_if_recursion_tail_stop:N #1
    \prop_get:NnNTF \c_@@_shorthands_prop {#1} \l_@@_tmp_tl
      { \exp_after:wN \@@_prepare_signature:N \l_@@_tmp_tl }
      {
        \int_incr:N \l_@@_current_arg_int
        \@@_prepare_signature_add:N #1
      }
  }
%    \end{macrocode}
%  For each known argument type there is an appropriate function to actually
%  do the addition to the signature. These are separate for expandable and
%  standard functions, as the approaches are different. Of course, if the type
%  is not known at all then a fall-back is needed.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_prepare_signature_add:N #1
  {
    \cs_if_exist_use:cF
      {
         @@_add
         \bool_if:NT \l_@@_expandable_bool { _expandable }
         _type_  \token_to_str:N #1 :w
      }
      {
        \__msg_kernel_error:nnx { xparse } { unknown-argument-type }
          { \token_to_str:N #1 }
        \bool_if:NTF \l_@@_expandable_bool
          { \@@_add_expandable_type_m:w }
          { \@@_add_type_m:w }
      }
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \subsection{Setting up a standard signature}
%
% Each argument-adding function appends to the signature a grabber (and
% for some types, the delimiters or default value), except the one for
% \texttt{m} arguments.  These are collected and added to the signature
% all at once by \cs{@@_flush_m_args:}, called for every other argument
% type.  All of the functions then call the loop function
% \cs{@@_prepare_signature:N}.
%
% \begin{macro}{\@@_add_type_+:w}
%   Making the next argument long means setting the flag and knocking one back
%   off the total argument count. The \texttt{m} arguments are recorded here as
%   this has to be done for every case where there is then a long argument.
%    \begin{macrocode}
\cs_new_protected_nopar:cpn { @@_add_type_+:w }
  {
    \@@_flush_m_args:
    \bool_set_true:N \l_@@_long_bool
    \int_decr:N \l_@@_current_arg_int
    \@@_prepare_signature:N
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_add_type_>:w}
%   When a processor is found, the function \cs{@@_process_arg:n} is added
%   to the signature along with the processor code itself. When the signature
%   is used, the code will be added to an execution list by
%   \cs{@@_process_arg:n}. Here, the loop calls
%   \cs{@@_prepare_signature_bypass:N} rather than
%   \cs{@@_prepare_signature:N} so that the flag is not reset.
%    \begin{macrocode}
\cs_new_protected:cpn { @@_add_type_>:w } #1
  {
    \@@_flush_m_args:
    \bool_set_true:N \l_@@_processor_bool
    \int_decr:N \l_@@_current_arg_int
    \tl_put_right:Nn \l_@@_signature_tl { \@@_process_arg:n {#1} }
    \@@_prepare_signature_bypass:N
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_add_type_d:w, \@@_add_type_D:w}
%   To save on repeated code, \texttt{d} is actually turned into the same
%   grabber as is used by \texttt{D}, by putting the |-NoValue-| default in
%   the correct place.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_add_type_d:w #1#2
  { \exp_args:NNNo \@@_add_type_D:w #1 #2 \c_@@_no_value_tl }
\cs_new_protected:Npn \@@_add_type_D:w #1#2#3
  {
    \@@_flush_m_args:
    \@@_add_grabber_optional:N D
    \tl_put_right:Nn \l_@@_signature_tl { #1 #2 {#3} }
    \@@_prepare_signature:N
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_add_type_g:w}
%   The \texttt{g} type is simply an alias for \texttt{G} with the correct
%   default built-in.
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \@@_add_type_g:w
  { \exp_args:No \@@_add_type_G:w \c_@@_no_value_tl }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_add_type_G:w}
%   For the \texttt{G} type, the grabber and the default are added to the
%   signature.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_add_type_G:w #1
  {
    \@@_flush_m_args:
    \@@_add_grabber_optional:N G
    \tl_put_right:Nn \l_@@_signature_tl { {#1} }
    \@@_prepare_signature:N
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_add_type_k:w, \@@_add_type_K:w}
%   Similar to |d|/|D| type but just one token to store.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_add_type_k:w #1
  { \exp_args:NNo \@@_add_type_K:w #1 \c_@@_no_value_tl }
\cs_new_protected:Npn \@@_add_type_K:w #1#2
  {
    \@@_flush_m_args:
    \@@_add_grabber_optional:N K
    \tl_put_right:Nn \l_@@_signature_tl { #1 {#2} }
    \@@_prepare_signature:N
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\@@_add_type_l:w}
%   Finding \texttt{l} arguments is very simple: there is nothing to do
%   other than add the grabber.
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \@@_add_type_l:w
  {
    \@@_flush_m_args:
    \@@_add_grabber_mandatory:N l
    \@@_prepare_signature:N
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_add_type_m:w}
%   The \texttt{m} type is special as short arguments which are not
%   post-processed are simply counted at this stage. Thus there is a check
%   to see if either of these cases apply. If so, a one-argument grabber
%   is added to the signature. On the other hand, if a standard short
%   argument is required it is simply counted at this stage, to be
%   added later using \cs{@@_flush_m_args:}.
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \@@_add_type_m:w
  {
    \bool_if:nTF { \l_@@_long_bool || \l_@@_processor_bool }
      {
        \@@_flush_m_args:
        \@@_add_grabber_mandatory:N m
      }
      { \int_incr:N \l_@@_m_args_int }
    \@@_prepare_signature:N
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_add_type_r:w, \@@_add_type_R:w}
%   The \texttt{r}- and \texttt{R}-type arguments are very similar to the
%   \texttt{d}- and \texttt{D}-types.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_add_type_r:w #1#2
  { \exp_args:NNNo \@@_add_type_R:w #1 #2 \c_@@_no_value_tl }
\cs_new_protected:Npn \@@_add_type_R:w #1#2#3
  {
    \@@_flush_m_args:
    \@@_add_grabber_mandatory:N R
    \tl_put_right:Nn \l_@@_signature_tl { #1 #2 {#3} }
    \@@_prepare_signature:N
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_add_type_t:w}
%   Setting up a \texttt{t} argument means collecting one token for the test,
%   and adding it along with the grabber to the signature.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_add_type_t:w #1
  {
    \@@_flush_m_args:
    \@@_add_grabber_optional:N t
    \tl_put_right:Nn \l_@@_signature_tl {#1}
    \@@_prepare_signature:N
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_add_type_u:w}
%   At the set up stage, the \texttt{u} type argument is identical to the
%   \texttt{G} type except for the name of the grabber function.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_add_type_u:w #1
  {
    \@@_flush_m_args:
    \@@_add_grabber_mandatory:N u
    \tl_put_right:Nn \l_@@_signature_tl { {#1} }
    \@@_prepare_signature:N
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_add_type_v:w}
%   At this stage, the \texttt{v} argument is identical to \texttt{l}.
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \@@_add_type_v:w
  {
    \@@_flush_m_args:
    \@@_add_grabber_mandatory:N v
    \@@_prepare_signature:N
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_flush_m_args:}
%   As \texttt{m} arguments are simply counted, there is a need to add
%   them to the token register in a block. As this function can only
%   be called if something other than \texttt{m} turns up, the flag can
%   be switched here. The total number of mandatory arguments which
%   remain to be added to
%   the signature is also decreased by the appropriate amount.
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \@@_flush_m_args:
  {
    \int_compare:nNnT \l_@@_m_args_int > \c_zero
      {
        \tl_put_right:Nx \l_@@_signature_tl
          { \exp_not:c { @@_grab_m_ \int_use:N \l_@@_m_args_int :w } }
        \int_sub:Nn \l_@@_mandatory_args_int { \l_@@_m_args_int }
      }
    \int_zero:N \l_@@_m_args_int
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_add_grabber_mandatory:N}
% \begin{macro}{\@@_add_grabber_optional:N}
%   To keep the various checks needed in one place, adding the grabber to
%   the signature is done here. For mandatory arguments, the only question
%   is whether to add a long grabber. For optional arguments, there is
%   also a check to see if any mandatory arguments are still to be added.
%   This is used to determine whether to skip spaces or not where
%   searching for the argument.
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \@@_add_grabber_mandatory:N #1
  {
    \tl_put_right:Nx \l_@@_signature_tl
      {
        \exp_not:c
          { @@_grab_ #1 \bool_if:NT \l_@@_long_bool { _long } :w }
      }
    \bool_set_false:N \l_@@_long_bool
    \int_decr:N \l_@@_mandatory_args_int
  }
\cs_new_protected_nopar:Npn \@@_add_grabber_optional:N #1
  {
    \tl_put_right:Nx \l_@@_signature_tl
      {
        \exp_not:c
          {
            @@_grab_ #1
            \bool_if:NT \l_@@_long_bool { _long }
            \int_compare:nNnF \l_@@_mandatory_args_int > \c_zero
              { _trailing }
            :w
          }
      }
    \bool_set_false:N \l_@@_long_bool
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \subsection{Setting up expandable types}
%
% The approach here is not dissimilar to that for standard types, although
% types which are not supported in expandable functions give an error. There is
% also a need to define the per-function auxiliaries: this is done here, while
% the general grabbers are dealt with later.
%
% \begin{macro}{\@@_add_expandable_type_+:w}
%   Check that a plus is given only if it occurs for every argument.
%    \begin{macrocode}
\cs_new_protected_nopar:cpn { @@_add_expandable_type_+:w }
  {
    \bool_set_true:N \l_@@_long_bool
    \int_compare:nNnTF \l_@@_current_arg_int = \c_one
      { \bool_set_true:N \l_@@_all_long_bool }
      {
        \bool_if:NF \l_@@_all_long_bool
          { \__msg_kernel_error:nn { xparse } { inconsistent-long } }
      }
    \int_decr:N \l_@@_current_arg_int
    \@@_prepare_signature:N
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_add_expandable_type_>:w}
%   No processors in expandable arguments, so this issues an error.
%    \begin{macrocode}
\cs_new_protected:cpn { @@_add_expandable_type_>:w } #1
  {
    \__msg_kernel_error:nnx { xparse } { processor-in-expandable }
      { \token_to_str:c { \l_@@_function_tl } }
    \int_decr:N \l_@@_current_arg_int
    \@@_prepare_signature:N
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_add_expandable_type_d:w}
% \begin{macro}{\@@_add_expandable_type_D:w}
% \begin{macro}{\@@_add_expandable_type_D_aux:NNn}
% \begin{macro}{\@@_add_expandable_type_D_aux:Nn}
%   The set up for \texttt{d}- and \texttt{D}-type arguments is the same,
%   and involves constructing a rather complex auxiliary which is used
%   repeatedly when grabbing. There is an auxiliary here so that the
%   \texttt{R}-type can share code readily.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_add_expandable_type_d:w #1#2
  {
    \exp_args:NNNo
      \@@_add_expandable_type_D:w #1 #2 \c_@@_no_value_tl
  }
\cs_new_protected:Npn \@@_add_expandable_type_D:w #1#2
  {
    \tl_if_eq:nnTF {#1} {#2}
      {
        \@@_add_expandable_grabber_optional:n { D_alt }
        \@@_add_expandable_type_D_aux:Nn #1
      }
      {
        \@@_add_expandable_grabber_optional:n { D }
        \@@_add_expandable_type_D_aux:NNn #1#2
      }
  }
\cs_new_protected:Npn \@@_add_expandable_type_D_aux:NNn #1#2#3
  {
    \bool_if:NTF \l_@@_all_long_bool
      { \cs_set:cpx }
      { \cs_set_nopar:cpx }
      { \l_@@_expandable_aux_name_tl } ##1 ##2 #1 ##3 \q_@@ ##4 #2
      { ##1 {##2} {##3} {##4} }
    \tl_put_right:Nx \l_@@_signature_tl
      {
        \exp_not:c  { \l_@@_expandable_aux_name_tl }
        \exp_not:n { #1 #2 {#3} }
      }
    \bool_set_false:N \l_@@_long_bool
    \@@_prepare_signature:N
  }
%    \end{macrocode}
%  This route is needed if the two delimiting tokens are identical: in
%  contrast to the non-expandable route, the grabber here has to act
%  differently for this case.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_add_expandable_type_D_aux:Nn #1#2
  {
    \bool_if:NTF \l_@@_all_long_bool
      { \cs_set:cpx }
      { \cs_set_nopar:cpx }
      { \l_@@_expandable_aux_name_tl } ##1 #1 ##2 #1
      { ##1 {##2} }
    \tl_put_right:Nx \l_@@_signature_tl
      {
        \exp_not:c  { \l_@@_expandable_aux_name_tl }
        \exp_not:n { #1 {#2} }
      }
    \bool_set_false:N \l_@@_long_bool
    \@@_prepare_signature:N
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\@@_add_expandable_type_g:w}
% \begin{macro}{\@@_add_expandable_type_G:w}
%   These are not allowed at all, so there is a complaint and a fall-back.
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \@@_add_expandable_type_g:w
  {
    \__msg_kernel_error:nnx { xparse } { invalid-expandable-argument-type }
      { g }
    \@@_add_expandable_type_m:w
  }
\cs_new_protected_nopar:Npn \@@_add_expandable_type_G:w #1
  {
    \__msg_kernel_error:nnx { xparse } { invalid-expandable-argument-type }
      { G }
    \@@_add_expandable_type_m:w
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\@@_add_expandable_type_k:w}
% \begin{macro}{\@@_add_expandable_type_K:w}
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \@@_add_expandable_type_k:w #1
  {
    \exp_args:NNo
      \@@_add_expandable_type_K:w #1 \c_@@_no_value_tl
  }
\cs_new_protected_nopar:Npn \@@_add_expandable_type_K:w #1#2
  {
    \@@_add_expandable_grabber_optional:n { K }
    \bool_if:NTF \l_@@_all_long_bool
      { \cs_set:cpx }
      { \cs_set_nopar:cpx }
      { \l_@@_expandable_aux_name_tl } ##1 #1 ##2
      { ##1 {##2} }
    \tl_put_right:Nx \l_@@_signature_tl
      {
        \exp_not:c { \l_@@_expandable_aux_name_tl }
        \exp_not:n { #1 {#2} }
      }
    \bool_set_false:N \l_@@_long_bool
    \@@_prepare_signature:N
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\@@_add_expandable_type_l:w}
%   Invalid in expandable contexts (as the next left brace may have been
%   inserted by \pkg{xparse} due to a failed search for an optional argument).
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \@@_add_expandable_type_l:w
  {
    \__msg_kernel_error:nnx { xparse } { invalid-expandable-argument-type }
      { l }
    \@@_add_expandable_type_m:w
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_add_expandable_type_m:w}
%   Unlike the standard case, when working expandably each argument is always
%   grabbed separately unless the function takes only \texttt{m}-type
%   arguments. To deal with the latter case, the value of
%   \cs{l_@@_m_args_int} needs to be increased appropriately.
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \@@_add_expandable_type_m:w
  {
    \int_incr:N \l_@@_m_args_int
    \@@_add_expandable_grabber_mandatory:n { m }
    \bool_set_false:N \l_@@_long_bool
    \@@_prepare_signature:N
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_add_expandable_type_r:w}
% \begin{macro}{\@@_add_expandable_type_R:w}
%   The \texttt{r}- and \texttt{R}-types are very similar to \texttt{D}-type
%   arguments, and so the same internals are used.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_add_expandable_type_r:w #1#2
  {
    \exp_args:NNNo
      \@@_add_expandable_type_R:w #1 #2 \c_@@_no_value_tl
  }
\cs_new_protected:Npn \@@_add_expandable_type_R:w #1#2
  {
    \tl_if_eq:nnTF {#1} {#2}
      {
        \@@_add_expandable_grabber_mandatory:n { R_alt }
        \@@_add_expandable_type_D_aux:Nn #1
      }
      {
        \@@_add_expandable_grabber_mandatory:n { R }
        \@@_add_expandable_type_D_aux:NNn #1#2
      }
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\@@_add_expandable_type_t:w}
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \@@_add_expandable_type_t:w #1
  {
    \@@_add_expandable_grabber_optional:n { t }
    \bool_if:NTF \l_@@_all_long_bool
      { \cs_set:cpn }
      { \cs_set_nopar:cpn }
      { \l_@@_expandable_aux_name_tl } ##1 #1 {##1}
    \tl_put_right:Nx \l_@@_signature_tl
      {
        \exp_not:c { \l_@@_expandable_aux_name_tl }
        \exp_not:N #1
      }
    \bool_set_false:N \l_@@_long_bool
    \@@_prepare_signature:N
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_add_expandable_type_u:w}
%   Invalid in an expandable context as any preceding optional argument may
%   wrap part of the delimiter up in braces.
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \@@_add_expandable_type_u:w #1
  {
    \__msg_kernel_error:nnx { xparse } { invalid-expandable-argument-type }
      { u }
    \@@_add_expandable_type_m:w
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_add_expandable_type_v:w}
%   Another forbidden type.
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \@@_add_expandable_type_v:w
  {
    \__msg_kernel_error:nnx { xparse } { invalid-expandable-argument-type }
      { v }
    \@@_add_expandable_type_m:w
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}
%   {
%     \@@_add_expandable_grabber_mandatory:n,
%     \@@_add_expandable_grabber_optional:n
%   }
% \begin{macro}[aux]{\@@_add_expandable_long_check:}
%   Adding a grabber to the signature is very simple here, with only a test to
%   ensure that optional arguments still have mandatory ones to follow. This
%   is also a good place to check on the consistency of the long status of
%   arguments.
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \@@_add_expandable_grabber_mandatory:n #1
  {
    \@@_add_expandable_long_check:
    \tl_put_right:Nx \l_@@_signature_tl
      { \exp_not:c { @@_expandable_grab_ #1 :w } }
    \bool_set_false:N \l_@@_long_bool
    \int_decr:N \l_@@_mandatory_args_int
  }
\cs_new_protected_nopar:Npn \@@_add_expandable_grabber_optional:n #1
  {
    \@@_add_expandable_long_check:
    \int_compare:nNnF \l_@@_mandatory_args_int > \c_zero
      { \__msg_kernel_error:nn { xparse } { expandable-ending-optional } }
    \tl_put_right:Nx \l_@@_signature_tl
      { \exp_not:c { @@_expandable_grab_ #1 :w } }
    \bool_set_false:N \l_@@_long_bool
  }
\cs_new_protected_nopar:Npn \@@_add_expandable_long_check:
  {
    \bool_if:nT { \l_@@_all_long_bool && ! \l_@@_long_bool }
      { \__msg_kernel_error:nn { xparse } { inconsistent-long } }
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \subsection{Grabbing arguments}
%
% All of the grabbers follow the same basic pattern. The initial
% function sets up the appropriate information to define
% \cs{@@_grab_arg:w} to grab the argument. This means determining
% whether to use \cs{cs_set:Npn} or \cs{cs_set_nopar:Npn}, and for
% optional arguments whether to skip spaces. In all cases,
% \cs{@@_grab_arg:w} is then called to actually do the grabbing.
%
% \begin{macro}{\@@_grab_arg:w}
% \begin{macro}[aux]{\@@_grab_arg_auxi:w}
% \begin{macro}[aux]{\@@_grab_arg_auxii:w}
%   Each time an argument is actually grabbed, \pkg{xparse} defines a
%   function to do it. In that way, long arguments from previous functions
%   can be included in the definition of the grabber function, so that
%   it does not raise an error if not long. The generic function used
%   for this is reserved here. A couple of auxiliary functions are also
%   needed in various places.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_grab_arg:w { }
\cs_new_protected:Npn \@@_grab_arg_auxi:w { }
\cs_new_protected:Npn \@@_grab_arg_auxii:w { }
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\@@_grab_D:w}
% \begin{macro}{\@@_grab_D_long:w}
% \begin{macro}{\@@_grab_D_trailing:w}
% \begin{macro}{\@@_grab_D_long_trailing:w}
%   The generic delimited argument grabber. The auxiliary function does
%   a peek test before calling \cs{@@_grab_arg:w}, so that the
%   optional nature of the argument works as expected.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_grab_D:w #1#2#3#4 \l_@@_args_tl
  {
    \@@_grab_D_aux:NNnnNn #1 #2 {#3} {#4} \cs_set_protected_nopar:Npn
      { _ignore_spaces }
  }
\cs_new_protected:Npn \@@_grab_D_long:w #1#2#3#4 \l_@@_args_tl
  {
    \@@_grab_D_aux:NNnnNn #1 #2 {#3} {#4} \cs_set_protected:Npn
      { _ignore_spaces }
  }
\cs_new_protected:Npn \@@_grab_D_trailing:w #1#2#3#4 \l_@@_args_tl
  { \@@_grab_D_aux:NNnnNn #1 #2 {#3} {#4} \cs_set_protected_nopar:Npn { } }
\cs_new_protected:Npn \@@_grab_D_long_trailing:w #1#2#3#4 \l_@@_args_tl
  { \@@_grab_D_aux:NNnnNn #1 #2 {#3} {#4} \cs_set_protected:Npn { } }
%    \end{macrocode}
% \begin{macro}[aux]{\@@_grab_D_aux:NNnnNn}
% \begin{macro}[aux]{\@@_grab_D_aux:NNnN}
%   This is a bit complicated. The idea is that, in order to check for
%   nested optional argument tokens (\texttt{[[...]]} and so on) the
%   argument needs to be grabbed without removing any braces at all. If
%   this is not done, then cases like |[{[}]| fail. So after testing for
%   an optional argument, it is collected piece-wise. Inserting a quark
%   prevents loss of braces, and there is then a test to see if there are
%   nested delimiters to handle.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_grab_D_aux:NNnnNn #1#2#3#4#5#6
  {
    \@@_grab_D_aux:NNnN #1#2 {#4} #5
    \use:c { peek_meaning_remove #6 :NTF } #1
      { \@@_grab_arg:w }
      {
        \@@_add_arg:n {#3}
        #4 \l_@@_args_tl
      }
  }
%    \end{macrocode}
%   Inside the \enquote{standard} grabber, there is a test to see if the
%   grabbed argument is entirely enclosed by braces. There are a couple of
%   extra factors to allow for: the argument might be entirely empty, and
%   spaces at the start and end of the input must be retained around a brace
%   group. Also notice that a \emph{blank} argument might still contain
%   spaces.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_grab_D_aux:NNnN #1#2#3#4
  {
    \cs_set_protected_nopar:Npn \@@_grab_arg:w
      {
        \exp_after:wN #4 \l_@@_fn_tl ####1 #2
          {
            \tl_if_in:nnTF {####1} {#1}
              { \@@_grab_D_nested:NNnnN #1 #2 {####1} {#3} #4 }
              {
                \tl_if_blank:oTF { \use_none:n ####1 }
                  { \@@_add_arg:o { \use_none:n ####1 } }
                  {
                    \str_if_eq_x:nnTF
                      { \exp_not:o { \use_none:n ####1 } }
                      { { \exp_not:o { \use_ii:nnn ####1 \q_nil } } }
                      { \@@_add_arg:o { \use_ii:nn ####1 } }
                      { \@@_add_arg:o { \use_none:n ####1 } }
                  }
                #3 \l_@@_args_tl
              }
          }
%    \end{macrocode}
%   This section needs a little explanation. In order to avoid losing any
%   braces, a token needs to be inserted before the argument to be grabbed.
%   If the argument runs away because the closing token is missing then this
%   inserted token shows up in the terminal. Ideally, |#1| would therefore be
%   used directly, but that is no good as it will mess up the rest of the
%   grabber. Instead, a copy of |#1| with an altered category code is used,
%   as this will look right in the terminal but will not mess up the grabber.
%   The only issue then is that the category code of |#1| is unknown. So there
%   is a quick test to ensure that the inserted token can never be matched by
%   the grabber. (This assumes that |#1| and |#2| are not the same character
%   with different category codes, but that really should not happen in any
%   sensible document-level syntax.)
%    \begin{macrocode}
        \token_if_eq_catcode:NNTF + #1
          {
            \exp_after:wN \exp_after:wN \exp_after:wN
              \l_@@_fn_tl \char_generate:nn { `#1 } { 11 }
          }
          {
            \exp_after:wN \l_@@_fn_tl
            \token_to_str:N #1
          }
      }
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
% \begin{macro}[aux]{\@@_grab_D_nested:NNnnN}
% \begin{macro}[aux]{\@@_grab_D_nested:w}
% \begin{macro}{\l_@@_nesting_a_tl}
% \begin{macro}{\l_@@_nesting_b_tl}
% \begin{macro}{\q_@@}
%   Catching nested optional arguments means more work. The aim here is
%   to collect up each pair of optional tokens without \TeX{} helping out,
%   and without counting anything. The code above will already have
%   removed the leading opening token and a closing token, but the
%   wrong one. The aim is then to work through the material grabbed
%   so far and divide it up on each opening token, grabbing a closing
%   token to match (thus working in pairs). Once there are no opening
%   tokens, then there is a second check to see if there are any
%   opening tokens in the second part of the argument (for things
%   like |[][]|). Once everything has been found, the entire collected
%   material is added to the output as a single argument. The only tricky part
%   here is ensuring that any grabbing function that might run away is named
%   after the function currently being parsed and not after \pkg{xparse}. That
%   leads to some rather complex nesting! There is also a need to prevent the
%   loss of any braces, hence the insertion and removal of quarks along the
%   way.
%    \begin{macrocode}
\tl_new:N \l_@@_nesting_a_tl
\tl_new:N \l_@@_nesting_b_tl
\quark_new:N \q_@@
\cs_new_protected:Npn \@@_grab_D_nested:NNnnN #1#2#3#4#5
  {
    \tl_clear:N \l_@@_nesting_a_tl
    \tl_clear:N \l_@@_nesting_b_tl
    \exp_after:wN #5 \l_@@_fn_tl ##1 #1 ##2 \q_@@ ##3 #2
      {
        \tl_put_right:No \l_@@_nesting_a_tl { \use_none:n ##1 #1 }
        \tl_put_right:No \l_@@_nesting_b_tl { \use_i:nn #2 ##3 }
        \tl_if_in:nnTF {##2} {#1}
          {
            \l_@@_fn_tl
              \q_nil ##2 \q_@@ \ERROR
          }
          {
            \tl_put_right:Nx \l_@@_nesting_a_tl
              { \@@_grab_D_nested:w \q_nil ##2 \q_stop }
            \tl_if_in:NnTF \l_@@_nesting_b_tl {#1}
              {
                \tl_set_eq:NN \l_@@_tmp_tl \l_@@_nesting_b_tl
                \tl_clear:N \l_@@_nesting_b_tl
                \exp_after:wN \l_@@_fn_tl \exp_after:wN
                  \q_nil \l_@@_tmp_tl \q_nil \q_@@ \ERROR
              }
              {
                \tl_put_right:No \l_@@_nesting_a_tl
                  \l_@@_nesting_b_tl
                \@@_add_arg:V \l_@@_nesting_a_tl
                #4 \l_@@_args_tl
              }
          }
      }
    \l_@@_fn_tl #3 \q_nil \q_@@ \ERROR
  }
\cs_new:Npn \@@_grab_D_nested:w #1 \q_nil \q_stop
  { \exp_not:o { \use_none:n #1 } }
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\@@_grab_G:w}
% \begin{macro}{\@@_grab_G_long:w}
% \begin{macro}{\@@_grab_G_trailing:w}
% \begin{macro}{\@@_grab_G_long_trailing:w}
% \begin{macro}[aux]{\@@_grab_G_aux:nnNn}
%   Optional groups are checked by meaning, so that the same code will
%   work with, for example, Con\TeX{}t-like input.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_grab_G:w #1#2 \l_@@_args_tl
  {
    \@@_grab_G_aux:nnNn {#1} {#2} \cs_set_protected_nopar:Npn
      { _ignore_spaces }
  }
\cs_new_protected:Npn \@@_grab_G_long:w #1#2 \l_@@_args_tl
  {
    \@@_grab_G_aux:nnNn {#1} {#2} \cs_set_protected:Npn { _ignore_spaces }
  }
\cs_new_protected:Npn \@@_grab_G_trailing:w #1#2 \l_@@_args_tl
  { \@@_grab_G_aux:nnNn {#1} {#2} \cs_set_protected_nopar:Npn { } }
\cs_new_protected:Npn \@@_grab_G_long_trailing:w #1#2 \l_@@_args_tl
  { \@@_grab_G_aux:nnNn {#1} {#2} \cs_set_protected:Npn { } }
\cs_new_protected:Npn \@@_grab_G_aux:nnNn #1#2#3#4
  {
    \exp_after:wN #3 \l_@@_fn_tl ##1
      {
        \@@_add_arg:n {##1}
        #2 \l_@@_args_tl
      }
    \use:c { peek_meaning #4 :NTF } \c_group_begin_token
      { \l_@@_fn_tl }
      {
        \@@_add_arg:n {#1}
        #2 \l_@@_args_tl
      }
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\@@_grab_K:w, \@@_grab_K_long:w}
% \begin{macro}[aux]{\@@_grab_K_aux:nnnNn}
%   Look ahead at one token and if it matches grab an argument.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_grab_K:w #1#2#3 \l_@@_args_tl
  {
    \@@_grab_K_aux:nnnNn
      {#1} {#2} {#3}
      \cs_set_protected_nopar:Npn
      { _ignore_spaces }
  }
\cs_new_protected:Npn \@@_grab_K_long:w #1#2#3 \l_@@_args_tl
  {
    \@@_grab_K_aux:nnnNn
      {#1} {#2} {#3}
      \cs_set_protected:Npn
      { _ignore_spaces }
  }
\cs_new_protected:Npn \@@_grab_K_trailing:w #1#2#3 \l_@@_args_tl
  {
    \@@_grab_K_aux:nnnNn
      {#1} {#2} {#3}
      \cs_set_protected_nopar:Npn
      { }
  }
\cs_new_protected:Npn \@@_grab_K_long_trailing:w #1#2#3 \l_@@_args_tl
  {
    \@@_grab_K_aux:nnnNn
      {#1} {#2} {#3}
      \cs_set_protected:Npn
      { }
  }
\cs_new_protected:Npn \@@_grab_K_aux:nnnNn #1#2#3#4#5
 {
   \exp_after:wN #4 \l_@@_fn_tl ##1
     {
       \@@_add_arg:n {##1}
       #3 \l_@@_args_tl
     }
   \use:c { peek_meaning_remove #5 :NTF } #1
     { \l_@@_fn_tl }
     {
       \@@_add_arg:n {#2}
       #3 \l_@@_args_tl
     }
 }
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\@@_grab_l:w}
% \begin{macro}{\@@_grab_l_long:w}
% \begin{macro}[aux]{\@@_grab_l_aux:nN}
%   Argument grabbers for mandatory \TeX{} arguments are pretty simple.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_grab_l:w #1 \l_@@_args_tl
  { \@@_grab_l_aux:nN {#1} \cs_set_protected_nopar:Npn }
\cs_new_protected:Npn \@@_grab_l_long:w #1 \l_@@_args_tl
  { \@@_grab_l_aux:nN {#1} \cs_set_protected:Npn }
\cs_new_protected:Npn \@@_grab_l_aux:nN #1#2
  {
    \exp_after:wN #2 \l_@@_fn_tl ##1##
      {
        \@@_add_arg:n {##1}
        #1 \l_@@_args_tl
      }
    \l_@@_fn_tl
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\@@_grab_m:w}
% \begin{macro}{\@@_grab_m_long:w}
%   Collecting a single mandatory argument is quite easy.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_grab_m:w #1 \l_@@_args_tl
  {
    \exp_after:wN \cs_set_protected_nopar:Npn \l_@@_fn_tl ##1
      {
        \@@_add_arg:n {##1}
        #1 \l_@@_args_tl
      }
    \l_@@_fn_tl
  }
\cs_new_protected:Npn \@@_grab_m_long:w #1 \l_@@_args_tl
  {
    \exp_after:wN \cs_set_protected:Npn \l_@@_fn_tl ##1
      {
        \@@_add_arg:n {##1}
        #1 \l_@@_args_tl
      }
    \l_@@_fn_tl
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\@@_grab_m_1:w}
% \begin{macro}{\@@_grab_m_2:w}
% \begin{macro}{\@@_grab_m_3:w}
% \begin{macro}{\@@_grab_m_4:w}
% \begin{macro}{\@@_grab_m_5:w}
% \begin{macro}{\@@_grab_m_6:w}
% \begin{macro}{\@@_grab_m_7:w}
% \begin{macro}{\@@_grab_m_8:w}
%   Grabbing 1--8 mandatory arguments. We don't need to worry about
%   nine arguments as this is only possible if everything is
%   mandatory. Each function has an auxiliary so that \cs{par} tokens
%   from other arguments still work.
%    \begin{macrocode}
\cs_new_protected:cpn { @@_grab_m_1:w } #1 \l_@@_args_tl
  {
    \exp_after:wN \cs_set_protected_nopar:Npn \l_@@_fn_tl ##1
      {
        \tl_put_right:Nn \l_@@_args_tl { {##1} }
        #1 \l_@@_args_tl
      }
    \l_@@_fn_tl
  }
\cs_new_protected:cpn { @@_grab_m_2:w } #1 \l_@@_args_tl
  {
    \exp_after:wN \cs_set_protected_nopar:Npn \l_@@_fn_tl
      ##1##2
      {
        \tl_put_right:Nn \l_@@_args_tl { {##1} {##2} }
        #1 \l_@@_args_tl
      }
    \l_@@_fn_tl
  }
\cs_new_protected:cpn { @@_grab_m_3:w } #1 \l_@@_args_tl
  {
    \exp_after:wN \cs_set_protected_nopar:Npn \l_@@_fn_tl
      ##1##2##3
      {
        \tl_put_right:Nn \l_@@_args_tl { {##1} {##2} {##3} }
        #1 \l_@@_args_tl
      }
    \l_@@_fn_tl
  }
\cs_new_protected:cpn { @@_grab_m_4:w } #1 \l_@@_args_tl
  {
    \exp_after:wN \cs_set_protected_nopar:Npn \l_@@_fn_tl
      ##1##2##3##4
      {
        \tl_put_right:Nn \l_@@_args_tl { {##1} {##2} {##3} {##4} }
        #1 \l_@@_args_tl
      }
    \l_@@_fn_tl
  }
\cs_new_protected:cpn { @@_grab_m_5:w } #1 \l_@@_args_tl
  {
    \exp_after:wN \cs_set_protected_nopar:Npn \l_@@_fn_tl
      ##1##2##3##4##5
      {
        \tl_put_right:Nn \l_@@_args_tl { {##1} {##2} {##3} {##4} {##5} }
        #1 \l_@@_args_tl
      }
    \l_@@_fn_tl
  }
\cs_new_protected:cpn { @@_grab_m_6:w } #1 \l_@@_args_tl
  {
    \exp_after:wN \cs_set_protected_nopar:Npn \l_@@_fn_tl
      ##1##2##3##4##5##6
      {
        \tl_put_right:Nn \l_@@_args_tl
          { {##1} {##2} {##3} {##4} {##5} {##6} }
        #1 \l_@@_args_tl
      }
    \l_@@_fn_tl
  }
\cs_new_protected:cpn { @@_grab_m_7:w } #1 \l_@@_args_tl
  {
    \exp_after:wN \cs_set_protected_nopar:Npn \l_@@_fn_tl
      ##1##2##3##4##5##6##7
      {
        \tl_put_right:Nn \l_@@_args_tl
          { {##1} {##2} {##3} {##4} {##5} {##6} {##7} }
        #1 \l_@@_args_tl
      }
    \l_@@_fn_tl
  }
\cs_new_protected:cpn { @@_grab_m_8:w } #1 \l_@@_args_tl
  {
    \exp_after:wN \cs_set_protected_nopar:Npn \l_@@_fn_tl
      ##1##2##3##4##5##6##7##8
      {
        \tl_put_right:Nn \l_@@_args_tl
          { {##1} {##2} {##3} {##4} {##5} {##6} {##7} {##8} }
        #1 \l_@@_args_tl
      }
    \l_@@_fn_tl
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\@@_grab_R:w, \@@_grab_R_long:w}
% \begin{macro}[aux]{\@@_grab_R_aux:NNnnN}
%  The grabber for \texttt{R}-type arguments is basically the same as
%  that for \texttt{D}-type ones, but always skips spaces (as it is mandatory)
%  and has a hard-coded error message.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_grab_R:w #1#2#3#4 \l_@@_args_tl
  { \@@_grab_R_aux:NNnnN #1 #2 {#3} {#4} \cs_set_protected_nopar:Npn }
\cs_new_protected:Npn \@@_grab_R_long:w #1#2#3#4 \l_@@_args_tl
  { \@@_grab_R_aux:NNnnN #1 #2 {#3} {#4} \cs_set_protected:Npn }
\cs_new_protected:Npn \@@_grab_R_aux:NNnnN #1#2#3#4#5
  {
    \@@_grab_D_aux:NNnN #1 #2 {#4} #5
    \peek_meaning_remove_ignore_spaces:NTF #1
      { \@@_grab_arg:w }
      {
        \__msg_kernel_error:nnxx { xparse } { missing-required }
          { \token_to_str:N #1 } { \tl_to_str:n {#3} }
        \@@_add_arg:n {#3}
        #4 \l_@@_args_tl
      }
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\@@_grab_t:w}
% \begin{macro}{\@@_grab_t_long:w}
% \begin{macro}{\@@_grab_t_trailing:w}
% \begin{macro}{\@@_grab_t_long_trailing:w}
% \begin{macro}[aux]{\@@_grab_t_aux:NnNn}
%   Dealing with a token is quite easy. Check the match, remove the
%   token if needed and add a flag to the output.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_grab_t:w #1#2 \l_@@_args_tl
  {
    \@@_grab_t_aux:NnNn #1 {#2} \cs_set_protected_nopar:Npn
      { _ignore_spaces }
  }
\cs_new_protected:Npn \@@_grab_t_long:w #1#2 \l_@@_args_tl
  { \@@_grab_t_aux:NnNn #1 {#2} \cs_set_protected:Npn { _ignore_spaces } }
\cs_new_protected:Npn \@@_grab_t_trailing:w #1#2 \l_@@_args_tl
  { \@@_grab_t_aux:NnNn #1 {#2} \cs_set_protected_nopar:Npn { } }
\cs_new_protected:Npn \@@_grab_t_long_trailing:w #1#2 \l_@@_args_tl
  { \@@_grab_t_aux:NnNn #1 {#2} \cs_set_protected:Npn { } }
\cs_new_protected:Npn \@@_grab_t_aux:NnNn #1#2#3#4
  {
    \exp_after:wN #3 \l_@@_fn_tl
      {
        \use:c { peek_meaning_remove #4 :NTF } #1
          {
            \@@_add_arg:n { \BooleanTrue }
            #2 \l_@@_args_tl
          }
          {
            \@@_add_arg:n { \BooleanFalse }
            #2 \l_@@_args_tl
          }
      }
    \l_@@_fn_tl
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\@@_grab_u:w}
% \begin{macro}{\@@_grab_u_long:w}
% \begin{macro}[aux]{\@@_grab_u_aux:nnN}
%   Grabbing up to a list of tokens is quite easy: define the grabber,
%   and then collect.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_grab_u:w #1#2 \l_@@_args_tl
  { \@@_grab_u_aux:nnN {#1} {#2} \cs_set_protected_nopar:Npn }
\cs_new_protected:Npn \@@_grab_u_long:w #1#2 \l_@@_args_tl
  { \@@_grab_u_aux:nnN {#1} {#2} \cs_set_protected:Npn }
\cs_new_protected:Npn \@@_grab_u_aux:nnN #1#2#3
  {
    \exp_after:wN #3 \l_@@_fn_tl ##1 #1
      {
        \@@_add_arg:n {##1}
        #2 \l_@@_args_tl
      }
    \l_@@_fn_tl
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\@@_grab_v:w}
% \begin{macro}{\@@_grab_v_long:w}
% \begin{macro}{\@@_grab_v_aux:w}
% \begin{macro}{\@@_grab_v_group_end:}
% \begin{variable}{\l_@@_v_rest_of_signature_tl}
% \begin{variable}{\l_@@_v_arg_tl}
%   The opening delimiter is the first non-space token, and is never
%   read verbatim.  This is required by consistency with the case where
%   the preceding argument was optional and absent: then \TeX{} has
%   already read and tokenized that token when looking for the optional
%   argument.  The first thing is thus to check is that this delimiter
%   is a character, and to distinguish the case of a left brace (in that
%   case, \cs{group_align_safe_end:} is needed to compensate for the
%   begin-group character that was just seen).  Then set verbatim
%   catcodes with \cs{@@_grab_v_aux_catcodes:}.
%
%   The group keep catcode changes local, and
%   \cs{group_align_safe_begin/end:} allow to use a character
%   with category code~$4$ (normally |&|) as the delimiter.
%   It is ended by \cs{@@_grab_v_group_end:}, which smuggles
%   the collected argument out of the group.
%    \begin{macrocode}
\tl_new:N \l_@@_v_rest_of_signature_tl
\tl_new:N \l_@@_v_arg_tl
\cs_new_protected_nopar:Npn \@@_grab_v:w
  {
    \bool_set_false:N \l_@@_long_bool
    \@@_grab_v_aux:w
  }
\cs_new_protected_nopar:Npn \@@_grab_v_long:w
  {
    \bool_set_true:N \l_@@_long_bool
    \@@_grab_v_aux:w
  }
\cs_new_protected:Npn \@@_grab_v_aux:w #1 \l_@@_args_tl
  {
    \tl_set:Nn \l_@@_v_rest_of_signature_tl {#1}
    \group_begin:
      \group_align_safe_begin:
        \tex_escapechar:D = 92 \scan_stop:
        \tl_clear:N \l_@@_v_arg_tl
        \peek_meaning_remove_ignore_spaces:NTF \c_group_begin_token
          {
            \group_align_safe_end:
            \@@_grab_v_bgroup:
          }
          {
            \peek_N_type:TF
              { \@@_grab_v_aux_test:N }
              { \@@_grab_v_aux_abort:n { } }
          }
  }
\cs_new_protected_nopar:Npn \@@_grab_v_group_end:
  {
        \group_align_safe_end:
        \exp_args:NNNo
      \group_end:
    \tl_set:Nn \l_@@_v_arg_tl { \l_@@_v_arg_tl }
  }
%    \end{macrocode}
% \end{variable}
% \end{variable}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\@@_grab_v_aux_test:N}
% \begin{macro}
%   {
%     \@@_grab_v_aux_loop:N,
%     \@@_grab_v_aux_loop:NN,
%     \@@_grab_v_aux_loop_end:
%   }
%   Check that the opening delimiter is a character, setup category codes,
%   then start reading tokens one by one, keeping the delimiter as an argument.
%   If the verbatim was not nested, we will be grabbing one character
%   at each step. Unfortunately, it can happen that what follows the
%   verbatim argument is already tokenized. Thus, we check at each step
%   that the next token is indeed a \enquote{nice}
%   character, \emph{i.e.}, is not a character with
%   category code $1$ (begin-group), $2$ (end-group)
%   or $6$ (macro parameter), nor the space character,
%   with category code~$10$ and character code~$32$,
%   nor a control sequence.
%   The partially built argument is stored in \cs{l_@@_v_arg_tl}.
%   If we ever meet a token which we cannot grab (non-N-type),
%   or which is not a character according to
%   \cs{@@_grab_v_token_if_char:NTF}, then we bail out with
%   \cs{@@_grab_v_aux_abort:n}. Otherwise, we stop at the first
%   character matching the delimiter.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_grab_v_aux_test:N #1
  {
    \@@_grab_v_token_if_char:NTF #1
      {
        \@@_grab_v_aux_put:N #1
        \@@_grab_v_aux_catcodes:
        \@@_grab_v_aux_loop:N #1
      }
      { \@@_grab_v_aux_abort:n {#1} #1 }
  }
\cs_new_protected:Npn \@@_grab_v_aux_loop:N #1
  {
    \peek_N_type:TF
      { \@@_grab_v_aux_loop:NN #1 }
      { \@@_grab_v_aux_abort:n { } }
  }
\cs_new_protected:Npn \@@_grab_v_aux_loop:NN #1#2
  {
    \@@_grab_v_token_if_char:NTF #2
      {
        \token_if_eq_charcode:NNTF #1 #2
          { \@@_grab_v_aux_loop_end: }
          {
            \@@_grab_v_aux_put:N #2
            \@@_grab_v_aux_loop:N #1
          }
      }
      { \@@_grab_v_aux_abort:n {#2} #2 }
  }
\cs_new_protected_nopar:Npn \@@_grab_v_aux_loop_end:
  {
    \@@_grab_v_group_end:
    \exp_args:Nx \@@_add_arg:n { \tl_tail:N \l_@@_v_arg_tl }
    \l_@@_v_rest_of_signature_tl \l_@@_args_tl
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\@@_grab_v_bgroup:}
% \begin{macro}{\@@_grab_v_bgroup_loop:}
% \begin{macro}{\@@_grab_v_bgroup_loop:N}
% \begin{variable}{\l_@@_v_nesting_int}
%   If the opening delimiter is a left brace, we keep track of
%   how many left and right braces were encountered so far in
%   \cs{l_@@_v_nesting_int} (the methods used for optional
%   arguments cannot apply here), and stop as soon as it reaches~$0$.
%
%   Some care was needed when removing the opening delimiter, which
%   has already been assigned category code~$1$: using
%   \cs{peek_meaning_remove:NTF} in the \cs{@@_grab_v_aux:w}
%   function would break within alignments. Instead, we first
%   convert that token to a string, and remove the result as a
%   normal undelimited argument.
%    \begin{macrocode}
\int_new:N \l_@@_v_nesting_int
\cs_new_protected_nopar:Npx \@@_grab_v_bgroup:
  {
    \exp_not:N \@@_grab_v_aux_catcodes:
    \exp_not:n { \int_set_eq:NN \l_@@_v_nesting_int \c_one }
    \exp_not:N \@@_grab_v_aux_put:N \iow_char:N \{
    \exp_not:N \@@_grab_v_bgroup_loop:
  }
\cs_new_protected:Npn \@@_grab_v_bgroup_loop:
  {
    \peek_N_type:TF
      { \@@_grab_v_bgroup_loop:N }
      { \@@_grab_v_aux_abort:n { } }
  }
\cs_new_protected:Npn \@@_grab_v_bgroup_loop:N #1
  {
    \@@_grab_v_token_if_char:NTF #1
      {
        \token_if_eq_charcode:NNTF \c_group_end_token #1
          {
            \int_decr:N \l_@@_v_nesting_int
            \int_compare:nNnTF \l_@@_v_nesting_int > \c_zero
              {
                \@@_grab_v_aux_put:N #1
                \@@_grab_v_bgroup_loop:
              }
              { \@@_grab_v_aux_loop_end: }
          }
          {
            \token_if_eq_charcode:NNT \c_group_begin_token #1
              { \int_incr:N \l_@@_v_nesting_int }
            \@@_grab_v_aux_put:N #1
            \@@_grab_v_bgroup_loop:
          }
      }
      { \@@_grab_v_aux_abort:n {#1} #1 }
  }
%    \end{macrocode}
% \end{variable}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\@@_grab_v_aux_catcodes:}
% \begin{macro}{\@@_grab_v_aux_abort:n}
%   In a standalone format, the list of special characters is kept
%   as a sequence, \cs{c_@@_special_chars_seq}, and we use
%   \tn{dospecials} in package mode.
%   The approach for short verbatim arguments is to make the end-line
%   character a macro parameter character: this is forbidden by the
%   rest of the code. Then the error branch can check what caused the
%   bail out and give the appropriate error message.
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \@@_grab_v_aux_catcodes:
  {
%<*initex>
    \seq_map_function:NN
      \c_@@_special_chars_seq
      \char_set_catcode_other:N
%</initex>
%<*package>
    \cs_set_eq:NN \do \char_set_catcode_other:N
    \dospecials
%</package>
    \tex_endlinechar:D = `\^^M \scan_stop:
    \bool_if:NTF \l_@@_long_bool
      { \char_set_catcode_other:n { \tex_endlinechar:D } }
      { \char_set_catcode_parameter:n { \tex_endlinechar:D } }
  }
\cs_new_protected:Npn \@@_grab_v_aux_abort:n #1
  {
    \@@_grab_v_group_end:
    \@@_add_arg:o \c_@@_no_value_tl
    \exp_after:wN \exp_after:wN \exp_after:wN
      \peek_meaning_remove:NTF \char_generate:nn { \tex_endlinechar:D } { 6 }
      {
        \__msg_kernel_error:nnxxx { xparse } { verbatim-newline }
          { \exp_after:wN \token_to_str:N \l_@@_fn_tl }
          { \tl_to_str:N \l_@@_v_arg_tl }
          { \tl_to_str:n {#1} }
        \l_@@_v_rest_of_signature_tl \l_@@_args_tl
      }
      {
        \__msg_kernel_error:nnxxx { xparse } { verbatim-tokenized }
          { \exp_after:wN \token_to_str:N \l_@@_fn_tl }
          { \tl_to_str:N \l_@@_v_arg_tl }
          { \tl_to_str:n {#1} }
        \l_@@_v_rest_of_signature_tl \l_@@_args_tl
      }
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\@@_grab_v_aux_put:N}
%   Storing one token in the collected argument. Most tokens are
%   converted to category code $12$, with the exception of active
%   characters, and spaces (not sure what should be done for those).
%    \begin{macrocode}
\cs_new_protected:Npn \@@_grab_v_aux_put:N #1
  {
    \tl_put_right:Nx \l_@@_v_arg_tl
      {
        \token_if_active:NTF #1
          { \exp_not:N #1 } { \token_to_str:N #1 }
      }
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_grab_v_token_if_char:NTF}
%   This function assumes that the escape character is printable.
%   Then the string representation of control sequences is at least
%   two characters, and \cs{str_tail:n} only removes the escape
%   character. Macro parameter characters are doubled by
%   \cs{tl_to_str:n}, and will also yield a non-empty result,
%   hence are not considered as characters.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_grab_v_token_if_char:NTF #1
  { \str_if_eq_x:nnTF { } { \str_tail:n {#1} } }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_add_arg:n, \@@_add_arg:V, \@@_add_arg:o}
% \begin{macro}[aux]{\@@_add_arg_aux:n, \@@_add_arg_aux:V}
%   The argument-storing system provides a single point for interfacing
%   with processors. They are done in a loop, counting downward. In this
%   way, the processor which was found last is executed first. The result
%   is that processors apply from right to left, as intended. Notice that
%   a set of braces are added back around the result of processing so that
%   the internal function will correctly pick up one argument for each
%   input argument.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_add_arg:n #1
  {
    \int_compare:nNnTF \l_@@_processor_int = \c_zero
      { \tl_put_right:Nn \l_@@_args_tl { {#1} } }
      {
        \tl_clear:N \ProcessedArgument
        \@@_if_no_value:nTF {#1}
          {
            \int_zero:N \l_@@_processor_int
            \tl_put_right:Nn \l_@@_args_tl { {#1} }
          }
          { \@@_add_arg_aux:n {#1} }
      }
  }
\cs_generate_variant:Nn \@@_add_arg:n { V , o }
\cs_new_protected:Npn \@@_add_arg_aux:n #1
  {
    \use:c { @@_processor_ \int_use:N \l_@@_processor_int :n } {#1}
    \int_decr:N \l_@@_processor_int
    \int_compare:nNnTF \l_@@_processor_int = \c_zero
      {
        \tl_put_right:Nx \l_@@_args_tl
          { { \exp_not:V \ProcessedArgument } }
      }
      { \@@_add_arg_aux:V \ProcessedArgument }
}
\cs_generate_variant:Nn \@@_add_arg_aux:n { V }
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \subsection{Grabbing arguments expandably}
%
% \begin{macro}[EXP]{\@@_expandable_grab_D:w}
% \begin{macro}[EXP, aux]{\@@_expandable_grab_D:NNNnwN}
% \begin{macro}[EXP, aux]{\@@_expandable_grab_D:NNNwNnnn}
% \begin{macro}[EXP, aux]{\@@_expandable_grab_D:Nw}
% \begin{macro}[EXP, aux]{\@@_expandable_grab_D:nnNNNwN}
%   The first step is to grab the first token or group. The generic grabber
%   \cs{\meta{function}}\verb*| | is just after \cs{q_@@}, we go and find
%   it.
%    \begin{macrocode}
\cs_new:Npn \@@_expandable_grab_D:w #1 \q_@@ #2
  { #2 { \@@_expandable_grab_D:NNNnwNn #1 \q_@@ #2 } }
%    \end{macrocode}
%   We then wish to test whether |#7|, which we just grabbed, is exactly |#2|.
%   Expand the only grabber function we have, |#1|, once: the two strings below
%   are equal if and only if |#7| matches |#2| exactly.\footnote{It is obvious
%   that if \texttt{\#7} matches \texttt{\#2} then the strings are equal. We
%   must check the converse. The right-hand-side of \cs{str_if_eq:onTF} does
%   not end with \texttt{\#3}, implying that the grabber function took
%   everything as its arguments. The first brace group can only be empty if
%   \texttt{\#7} starts with \texttt{\#2}, otherwise the brace group preceding
%   \texttt{\#7} would not vanish. The third brace group is empty, thus the
%   \cs{q_@@} that was used by our grabber \texttt{\#1} must be the one
%   that we inserted (not some token in \texttt{\#7}), hence the second brace
%   group contains the end of \texttt{\#7} followed by \texttt{\#2}. Since this
%   is \texttt{\#2} on the right-hand-side, and no brace can be lost there,
%   \texttt{\#7} must contain nothing else than its leading \texttt{\#2}.} If
%   |#7| does not match |#2|, then the optional argument is missing, we use the
%   default |#4|, and put back the argument |#7| in the input stream.
%   %^^A There is probably a bug similar to the non-expandable O{\par} bug.
%
%   If it does match, then interesting things need to be done. We will grab the
%   argument piece by piece, with the following pattern:
%   \begin{quote}
%     \meta{grabber} \Arg{tokens} \\
%     ~~\cs{q_nil} \Arg{piece 1} \meta{piece 2} \cs{ERROR} \cs{q_@@}\\
%     ~~\cs{q_nil} \meta{input stream}
%   \end{quote}
%   The \meta{grabber} will find an opening delimiter in \meta{piece 2}, take
%   the \cs{q_@@} as a second delimiter, and find more material delimited
%   by the closing delimiter in the \meta{input stream}. We then move the part
%   before the opening delimiter from \meta{piece 2} to \meta{piece 1}, and the
%   material taken from the \meta{input stream} to the \meta{piece 2}. Thus,
%   the argument moves gradually from the \meta{input stream} to the
%   \meta{piece 2}, then to the \meta{piece 1} when we have made sure to find
%   all opening and closing delimiters. This two-step process ensures that
%   nesting works: the number of opening delimiters minus closing delimiters in
%   \meta{piece 1} is always equal to the number of closing delimiters in
%   \meta{piece 2}. We stop grabbing arguments once the \meta{piece 2} contains
%   no opening delimiter any more, hence the balance is reached, and the final
%   argument is \meta{piece 1} \meta{piece 2}.
%    \begin{macrocode}
\cs_new:Npn \@@_expandable_grab_D:NNNnwNn #1#2#3#4#5 \q_@@ #6#7
  {
    \str_if_eq:onTF
      { #1 { } { } #7 #2 \q_@@ #3 }
      { { } {#2} { } }
      {
        #1
          { \@@_expandable_grab_D:NNNwNnnn #1#2#3#5 \q_@@ #6 }
          \q_nil { } #2 \ERROR \q_@@ \ERROR
      }
      { #5 {#4} \q_@@ #6 {#7} }
  }
%    \end{macrocode}
%   At this stage, |#6| is \cs{q_nil} \Arg{piece 1} \meta{more for piece 1},
%   and we want to concatenate all that, removing \cs{q_nil}, and keeping the
%   opening delimiter |#2|. Simply use \cs{use_ii:nn}. Also, |#7| is
%   \meta{remainder of piece 2} \cs{ERROR}, and |#8| is \cs{ERROR} \meta{more
%   for piece 2}. We concatenate those, replacing the two \cs{ERROR} by the
%   closing delimiter |#3|.
%    \begin{macrocode}
\cs_new:Npn \@@_expandable_grab_D:NNNwNnnn #1#2#3#4 \q_@@ #5#6#7#8
  {
    \exp_args:Nof \@@_expandable_grab_D:nnNNNwN
      { \use_ii:nn #6 #2 }
      { \@@_expandable_grab_D:Nw #3 \exp_stop_f: #7 #8 }
    #1#2#3 #4 \q_@@ #5
  }
\cs_new:Npn \@@_expandable_grab_D:Nw #1#2 \ERROR \ERROR { #2 #1 }
%    \end{macrocode}
%   Armed with our two new \meta{pieces}, we are ready to loop. However, we
%   must first see if \meta{piece 2} (here |#2|) contains any opening
%   delimiter |#4|. Again, we expand |#3|, this time removing its whole output
%   with \cs{use_none:nnn}. The test is similar to \cs{tl_if_in:nnTF}. The
%   token list is empty if and only if |#2| does not contain the opening
%   delimiter. In that case, we are done, and put the argument (from which we
%   remove a spurious pair of delimiters coming from how we started the loop).
%   Otherwise, we go back to looping with
%   \cs{@@_expandable_grab_D:NNNwNnnn}. The code to deal with brace stripping
%   is much the same as for the non-expandable case.
%    \begin{macrocode}
\cs_new:Npn \@@_expandable_grab_D:nnNNNwN #1#2#3#4#5#6 \q_@@ #7
  {
    \exp_args:No \tl_if_empty:oTF
      { #3 { \use_none:nnn } #2 \q_@@ #5 #4 \q_@@ #5 }
      {
        \tl_if_blank:oTF { \use_none:nn #1#2 }
          { \@@_put_arg_expandable:ow { \use_none:nn #1#2 } }
          {
            \str_if_eq_x:nnTF
              { \exp_not:o { \use_none:nn #1#2 } }
              { { \exp_not:o { \use_iii:nnnn #1#2 \q_nil } } }
              { \@@_put_arg_expandable:ow { \use_iii:nnn #1#2 } }
              { \@@_put_arg_expandable:ow { \use_none:nn #1#2 } }
          }
            #6 \q_@@ #7
      }
      {
        #3
          { \@@_expandable_grab_D:NNNwNnnn #3#4#5#6 \q_@@ #7 }
          \q_nil {#1} #2 \ERROR \q_@@ \ERROR
      }
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}[EXP]{\@@_expandable_grab_D_alt:w}
% \begin{macro}[EXP]{\@@_expandable_grab_D_alt:NNnwNn}
% \begin{macro}[EXP]{\@@_expandable_grab_D_alt:Nw}
%   When the delimiters are identical, nesting is not possible and a simplified
%   approach is used. The test concept here is the same as for the case where
%   the delimiters are different.
%    \begin{macrocode}
\cs_new:Npn \@@_expandable_grab_D_alt:w #1 \q_@@ #2
  { #2 { \@@_expandable_grab_D_alt:NNnwNn #1 \q_@@ #2 } }
\cs_new:Npn \@@_expandable_grab_D_alt:NNnwNn #1#2#3#4 \q_@@ #5#6
  {
    \str_if_eq:onTF
      { #1 { } #6 #2 #2 }
      { { } #2 }
      {
        #1
          { \@@_expandable_grab_D_alt:Nwn #5 #4 \q_@@ }
          #6 \ERROR
      }
      { #4 {#3} \q_@@ #5 {#6} }
  }
\cs_new:Npn \@@_expandable_grab_D_alt:Nwn #1#2 \q_@@ #3
  {
    \tl_if_blank:oTF { \use_none:n #3 }
      { \@@_put_arg_expandable:ow { \use_none:n #3 } }
      {
        \str_if_eq_x:nnTF
          { \exp_not:o { \use_none:n #3 } }
          { { \exp_not:o { \use_ii:nnn #3 \q_nil } } }
          { \@@_put_arg_expandable:ow { \use_ii:nn #3 } }
          { \@@_put_arg_expandable:ow { \use_none:n #3 } }
      }
        #2 \q_@@ #1
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}[EXP]{\@@_expandable_grab_K:w}
% \begin{macro}[EXP, aux]{\@@_expandable_grab_K_aux:NNwn}
%   As for the |D|-type grabber, use the auxiliary to do the look ahead
%   test then reuse it for the grabbing.
%    \begin{macrocode}
\cs_new:Npn \@@_expandable_grab_K:w #1 \q_@@ #2
  { #2 { \@@_expandable_grab_K_aux:NNwn #1 \q_@@ #2 } }
\cs_new:Npn \@@_expandable_grab_K_aux:NNwn #1#2#3#4 \q_@@ #5#6
  {
    \str_if_eq:onTF { #1 { } #6 { } #2 { } } { { } #2 { } }
      {
        #1
          { \@@_expandable_grab_K_aux:Nwn #5 #4 \q_@@ }
          #6
      }
      { #4 {#3} \q_@@ #5 {#6} }
  }
\cs_new:Npn \@@_expandable_grab_K_aux:Nwn #1#2 \q_@@ #3
  { #2 {#3} \q_@@ #1 }
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}[EXP]{\@@_expandable_grab_m:w}
% \begin{macro}[EXP, aux]{\@@_expandable_grab_m_aux:wNn}
%   The mandatory case is easy: find the auxiliary after the \cs{q_@@}, and
%   use it directly to grab the argument.
%    \begin{macrocode}
\cs_new:Npn \@@_expandable_grab_m:w #1 \q_@@ #2
  { #2 { \@@_expandable_grab_m_aux:wNn #1 \q_@@ #2 } }
\cs_new:Npn \@@_expandable_grab_m_aux:wNn #1 \q_@@ #2#3
  { #1 {#3} \q_@@ #2 }
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}[EXP]{\@@_expandable_grab_R:w}
% \begin{macro}[EXP, aux]{\@@_expandable_grab_R_aux:NNwn}
%   Much the same as for the \texttt{D}-type argument, with only the lead-off
%   function varying.
%    \begin{macrocode}
\cs_new:Npn \@@_expandable_grab_R:w #1 \q_@@ #2
  { #2 { \@@_expandable_grab_R_aux:NNNnwNn #1 \q_@@ #2 } }
\cs_new:Npn \@@_expandable_grab_R_aux:NNNnwNn #1#2#3#4#5 \q_@@ #6#7
  {
    \str_if_eq:onTF
      { #1 { } { } #7 #2 \q_@@ #3 }
      { { } {#2} { } }
      {
        #1
          { \@@_expandable_grab_D:NNNwNnnn #1#2#3#5 \q_@@ #6 }
          \q_nil { } #2 \ERROR \q_@@ \ERROR
      }
      {
        \__msg_kernel_expandable_error:nnn
          { xparse } { missing-required } {#2}
        #5 {#4} \q_@@ #6 {#7}
      }
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}[EXP]{\@@_expandable_grab_R_alt:w}
% \begin{macro}[EXP]{\@@_expandable_grab_R_alt_aux:NNnwNn}
%   When the delimiters are identical, nesting is not possible and a simplified
%   approach is used. The test concept here is the same as for the case where
%   the delimiters are different.
%    \begin{macrocode}
\cs_new:Npn \@@_expandable_grab_R_alt:w #1 \q_@@ #2
  { #2 { \@@_expandable_grab_R_alt_aux:NNnwNn #1 \q_@@ #2 } }
\cs_new:Npn \@@_expandable_grab_R_alt_aux:NNnwNn #1#2#3#4 \q_@@ #5#6
  {
    \str_if_eq:onTF
      { #1 { } #6 #2 #2 }
      { { } #2 }
      {
        #1
          { \@@_expandable_grab_D_alt:Nwn #5 #4 \q_@@ }
          #6 \ERROR
      }
      {
        \__msg_kernel_expandable_error:nnn
          { xparse } { missing-required } {#2}
        #4 {#3} \q_@@ #5 {#6}
      }
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}[EXP]{\@@_expandable_grab_t:w}
% \begin{macro}[EXP, aux]{\@@_expandable_grab_t_aux:NNwn}
%   As for a \texttt{D}-type argument, here we compare the grabbed tokens using
%   the only parser we have in order to work out if |#2| is exactly equal to
%   the output of the grabber.
%    \begin{macrocode}
\cs_new:Npn \@@_expandable_grab_t:w #1 \q_@@ #2
  { #2 { \@@_expandable_grab_t_aux:NNwn #1 \q_@@ #2 } }
\cs_new:Npn \@@_expandable_grab_t_aux:NNwn #1#2#3 \q_@@ #4#5
  {
    \str_if_eq:onTF { #1 { } #5 #2 } {#2}
      { #3 { \BooleanTrue } \q_@@ #4 }
      { #3 { \BooleanFalse } \q_@@ #4 {#5} }
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}[EXP]
%   {\@@_put_arg_expandable:nw, \@@_put_arg_expandable:ow}
%   A useful helper, to store arguments when they are ready.
%    \begin{macrocode}
\cs_new:Npn \@@_put_arg_expandable:nw #1#2 \q_@@ { #2 {#1} \q_@@ }
\cs_generate_variant:Nn \@@_put_arg_expandable:nw { o }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[EXP]{\@@_grab_expandable_end:wN}
%   For the end of the grabbing sequence: get rid of the generic grabber and
%   insert the code function followed by its arguments.
%    \begin{macrocode}
\cs_new:Npn \@@_grab_expandable_end:wN #1 \q_@@ #2 {#1}
%    \end{macrocode}
% \end{macro}
%
% \subsection{Argument processors}
%
% \begin{macro}{\@@_process_arg:n}
%   Processors are saved for use later during the grabbing process.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_process_arg:n #1
  {
    \int_incr:N \l_@@_processor_int
    \cs_set_protected:cpx
      { @@_processor_ \int_use:N \l_@@_processor_int :n } ##1
      { \exp_not:n {#1} {##1} }
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_bool_reverse:N}
%   A simple reversal.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_bool_reverse:N #1
  {
    \bool_if:NTF #1
      { \tl_set:Nn \ProcessedArgument { \c_false_bool } }
      { \tl_set:Nn \ProcessedArgument { \c_true_bool } }
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{variable}{\l_@@_split_list_seq, \l_@@_split_list_tl}
% \begin{macro}{\@@_split_list:nn}
% \begin{macro}[aux]{\@@_split_list_multi:nn, \@@_split_list_multi:nV}
% \begin{macro}[aux]{\@@_split_list_single:Nn}
%   Splitting can take place either at a single token or at a longer
%   identifier. To deal with single active tokens, a two-part procedure is
%   needed.
%    \begin{macrocode}
\seq_new:N \l_@@_split_list_seq
\tl_new:N \l_@@_split_list_tl
\cs_new_protected:Npn \@@_split_list:nn #1#2
  {
    \tl_if_single:nTF {#1}
      {
        \token_if_cs:NTF #1
          { \@@_split_list_multi:nn {#1} {#2} }
          { \@@_split_list_single:Nn #1 {#2} }
      }
      { \@@_split_list_multi:nn {#1} {#2} }
  }
\cs_new_protected:Npn \@@_split_list_multi:nn #1#2
  {
    \seq_set_split:Nnn \l_@@_split_list_seq {#1} {#2}
    \tl_clear:N \ProcessedArgument
    \seq_map_inline:Nn \l_@@_split_list_seq
      { \tl_put_right:Nn \ProcessedArgument { {##1} } }
  }
\cs_generate_variant:Nn \@@_split_list_multi:nn { nV }
\group_begin:
\char_set_catcode_active:N \^^@
\cs_new_protected:Npn \@@_split_list_single:Nn #1#2
  {
    \tl_set:Nn \l_@@_split_list_tl {#2}
    \group_begin:
    \char_set_lccode:nn { `\^^@ } { `#1 }
    \tex_lowercase:D
      {
        \group_end:
        \tl_replace_all:Nnn \l_@@_split_list_tl { ^^@ }
      }   {#1}
     \@@_split_list_multi:nV {#1} \l_@@_split_list_tl
   }
\group_end:
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{variable}
%
% \begin{macro}{\@@_split_argument:nnn}
% \begin{macro}[aux]{\@@_split_argument_aux:nnnn}
% \begin{macro}[aux, EXP]{\@@_split_argument_aux:n}
% \begin{macro}[aux, rEXP]{\@@_split_argument_aux:wn}
%   Splitting to a known number of items is a special version of splitting
%   a list, in which the limit is hard-coded and where there will always be
%   exactly the correct number of output items. An auxiliary function is
%   used to save on working out the token list length several times.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_split_argument:nnn #1#2#3
  {
    \@@_split_list:nn {#2} {#3}
    \exp_args:Nf \@@_split_argument_aux:nnnn
      { \tl_count:N \ProcessedArgument }
      {#1} {#2} {#3}
  }
\cs_new_protected:Npn \@@_split_argument_aux:nnnn #1#2#3#4
  {
    \int_compare:nNnF {#1} = { #2 + \c_one }
      {
        \int_compare:nNnTF {#1} > { #2 + \c_one }
          {
            \tl_set:Nx \ProcessedArgument
              {
                \exp_last_unbraced:NnNo
                  \@@_split_argument_aux:n
                  { #2 + \c_one }
                  \use_none_delimit_by_q_stop:w
                  \ProcessedArgument
                  \q_stop
              }
            \__msg_kernel_error:nnxxx { xparse } { split-excess-tokens }
              { \tl_to_str:n {#3} } { \int_eval:n { #2 + \c_one } }
              { \tl_to_str:n {#4} }
          }
          {
            \tl_put_right:Nx \ProcessedArgument
              {
                \prg_replicate:nn { #2 + \c_one - (#1) }
                  { { \exp_not:V \c_@@_no_value_tl } }
              }
          }
      }
  }
%    \end{macrocode}
%   Auxiliaries to leave exactly the correct number of arguments in
%   \cs{ProcessedArgument}.
%    \begin{macrocode}
\cs_new:Npn \@@_split_argument_aux:n #1
  { \prg_replicate:nn {#1} { \@@_split_argument_aux:wn } }
\cs_new:Npn \@@_split_argument_aux:wn #1 \use_none_delimit_by_q_stop:w #2
  {
    \exp_not:n { {#2} }
    #1
    \use_none_delimit_by_q_stop:w
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\@@_trim_spaces:n}
%   This one is almost trivial.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_trim_spaces:n #1
  { \tl_set:Nx \ProcessedArgument { \tl_trim_spaces:n {#1} } }
%    \end{macrocode}
% \end{macro}
%
% \subsection{Access to the argument specification}
%
% \begin{macro}{\@@_get_arg_spec_error:N, \@@_get_arg_spec_error:n}
%   Provide an informative error when trying to get the argument
%   specification of a non-\pkg{xparse} command or environment.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_get_arg_spec_error:N #1
  {
    \cs_if_exist:NTF #1
      {
        \__msg_kernel_error:nnx { xparse } { non-xparse-command }
          { \token_to_str:N #1 }
      }
      {
        \__msg_kernel_error:nnx { xparse } { unknown-command }
          { \token_to_str:N #1 }
      }
  }
\cs_new_protected:Npn \@@_get_arg_spec_error:n #1
  {
    \cs_if_exist:cTF {#1}
      {
        \__msg_kernel_error:nnx { xparse } { non-xparse-environment }
          { \tl_to_str:n {#1} }
      }
      {
        \__msg_kernel_error:nnx { xparse } { unknown-environment }
          { \tl_to_str:n {#1} }
      }
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_get_arg_spec:N}
% \begin{macro}{\@@_get_arg_spec:n}
% \begin{variable}{\ArgumentSpecification}
%   Recovering the argument specification is trivial, using the
%   branching \cs{prop_get:NnN} function.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_get_arg_spec:N #1
  {
    \prop_get:NnNF \l_@@_command_arg_specs_prop {#1}
      \ArgumentSpecification
      { \@@_get_arg_spec_error:N #1 }
  }
\cs_new_protected:Npn \@@_get_arg_spec:n #1
  {
    \prop_get:NnNF \l_@@_environment_arg_specs_prop {#1}
      \ArgumentSpecification
      { \@@_get_arg_spec_error:n {#1} }
  }
\tl_new:N \ArgumentSpecification
%    \end{macrocode}
% \end{variable}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\@@_show_arg_spec:N}
% \begin{macro}{\@@_show_arg_spec:n}
%   Showing the argument specification simply means finding it and then
%   calling the \cs{tl_show:N} function.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_show_arg_spec:N #1
  {
    \prop_get:NnNTF \l_@@_command_arg_specs_prop {#1}
      \ArgumentSpecification
      { \tl_show:N \ArgumentSpecification }
      { \@@_get_arg_spec_error:N #1 }
  }
\cs_new_protected:Npn \@@_show_arg_spec:n #1
  {
    \prop_get:NnNTF \l_@@_environment_arg_specs_prop {#1}
      \ArgumentSpecification
      { \tl_show:N \ArgumentSpecification }
      { \@@_get_arg_spec_error:n {#1} }
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \subsection{Utilities}
%
% \begin{macro}[TF]{\@@_if_no_value:n}
%   Tests for |-NoValue-|: this is similar to \cs{tl_if_in:nn} but set
%   up to be expandable and to check the value exactly.  The question
%   mark prevents the auxiliary from losing braces.
%    \begin{macrocode}
\use:x
  {
    \prg_new_conditional:Npnn \exp_not:N \@@_if_no_value:n ##1
      { T ,  F , TF }
      {
        \exp_not:N \str_if_eq:onTF
          {
            \exp_not:N \@@_if_value_aux:w ? ##1 { }
              \c_@@_no_value_tl
          }
          { ? { } \c_@@_no_value_tl }
          { \exp_not:N \prg_return_true: }
          { \exp_not:N \prg_return_false: }
      }
    \cs_new:Npn \exp_not:N \@@_if_value_aux:w ##1 \c_@@_no_value_tl
      {##1}
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_check_definable:nNT, \@@_check_definable_aux:nN}
%   Check that a token list is appropriate as a first argument of
%   \cs{DeclareDocumentCommand} and similar functions and otherwise
%   produce an error.  First trim whitespace to allow for spaces around
%   the actual command to be defined.  If the result has multiple
%   tokens, it is not a valid argument.  The single token is a control
%   sequence exactly if its string representation has more than one
%   character (using \cs{token_to_str:N} rather than \cs{tl_to_str:n}
%   to avoid problems with macro parameter characters, and setting
%   \cs{tex_escapechar:D} to prevent it from being non-printable).
%   Finally, check for an active character: this is done by lowercasing
%   the token to fix its character code (arbitrarily to that of~|?|)
%   and comparing the result to an active~|?|.  Both control sequences
%   and active characters are valid arguments, and non-active character
%   tokens are not.  In all cases, the group opened to keep assignments
%   local must be closed.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_check_definable:nNT #1
  { \exp_args:Nx \@@_check_definable_aux:nN { \tl_trim_spaces:n {#1} } }
\group_begin:
  \char_set_catcode_active:n { `? }
  \cs_new_protected:Npn \@@_check_definable_aux:nN #1#2
    {
      \group_begin:
      \tl_if_single_token:nTF {#1}
        {
          \int_set:Nn \tex_escapechar:D { 92 }
          \exp_args:Nx \tl_if_empty:nTF
            { \exp_args:No \str_tail:n { \token_to_str:N #1 } }
            {
              \exp_args:Nx \char_set_lccode:nn
                { ` \str_head:n {#1} } { `? }
              \tex_lowercase:D { \tl_if_eq:nnTF {#1} } { ? }
                { \group_end: \use_iii:nnn }
                { \group_end: \use_i:nnn }
            }
            { \group_end: \use_iii:nnn }
        }
        { \group_end: \use_ii:nnn }
      {
        \__msg_kernel_error:nnxx { xparse } { not-definable }
          { \tl_to_str:n {#1} } { \token_to_str:N #2 }
      }
      {
        \__msg_kernel_error:nnxx { xparse } { not-one-token }
          { \tl_to_str:n {#1} } { \token_to_str:N #2 }
      }
    }
\group_end:
%    \end{macrocode}
% \end{macro}
%
% \subsection{Messages}
%
% Some messages intended as errors.
%    \begin{macrocode}
\__msg_kernel_new:nnnn { xparse } { bad-arg-spec }
  { Bad~argument~specification~'#1'. }
  {
    \c__msg_coding_error_text_tl
    The~argument~specification~provided~was~not~valid:~
    one~or~more~mandatory~pieces~of~information~were~missing. \\ \\
    LaTeX~will~ignore~this~entire~definition.
  }
\__msg_kernel_new:nnnn { xparse } { command-already-defined }
  { Command~'#1'~already~defined! }
  {
    You~have~used~\NewDocumentCommand
    with~a~command~that~already~has~a~definition. \\
    The~existing~definition~of~'#1'~will~not~be~altered.
  }
\__msg_kernel_new:nnnn { xparse } { command-not-yet-defined }
  { Command ~'#1'~not~yet~defined! }
  {
    You~have~used~\RenewDocumentCommand
    with~a~command~that~was~never~defined. \\
    A~new~command~'#1'~will~be~created.
  }
\__msg_kernel_new:nnnn { xparse } { environment-already-defined }
  { Environment~'#1'~already~defined! }
  {
    You~have~used~\NewDocumentEnvironment
    with~an~environment~that~already~has~a~definition. \\
    The~existing~definition~of~'#1'~will~be~overwritten.
  }
\__msg_kernel_new:nnnn { xparse } { environment-not-yet-defined }
  { Environment~'#1'~not~yet~defined! }
  {
    You~have~used~\RenewDocumentEnvironment
    with~an~environment~that~was~never~defined. \\
    A~new~environment~'#1'~will~be~created.
  }
\__msg_kernel_new:nnnn { xparse } { expandable-ending-optional }
  {
    Argument~specification~for~expandable~command~ends~with~optional~argument.
  }
  {
    \c__msg_coding_error_text_tl
    Expandable~commands~must~have~a~final~mandatory~argument~
    (or~no~arguments~at~all).~You~cannot~have~a~terminal~optional~
    argument~with~expandable~commands.
  }
\__msg_kernel_new:nnnn { xparse } { inconsistent-long }
  { Inconsistent~long~arguments~for~expandable~command. }
  {
    \c__msg_coding_error_text_tl
    The~arguments~for~an~expandable~command~must~either~all~be~
    short~or~all~be~long.~You~have~tried~to~mix~the~two~types.
  }
\__msg_kernel_new:nnnn { xparse } { invalid-expandable-argument-type }
  { Argument~type~'#1'~not~available~for~an~expandable~function. }
  {
    \c__msg_coding_error_text_tl
    The~letter~'#1'~does~not~specify~an~argument~type~which~can~be~used~
    in~an~expandable~function.
    \\ \\
    LaTeX~will~assume~you~want~a~standard~mandatory~argument~(type~'m').
  }
\__msg_kernel_new:nnnn { xparse } { missing-required }
  { Failed~to~find~required~argument~starting~with~'#1'. }
  {
    There~is~supposed~to~be~an~argument~to~the~current~function~starting~with~
    '#1'.~LaTeX~did~not~find~it,~and~will~insert~'#2'~as~the~value~to~be~
    processed.
  }
\__msg_kernel_new:nnnn { xparse } { non-xparse-command }
  { Command~'#1'~not~defined~using~xparse. }
  {
    You~have~asked~for~the~argument~specification~for~a~command~'#1',~
    but~this~is~not~a~command~defined~using~xparse.
  }
\__msg_kernel_new:nnnn { xparse } { non-xparse-environment }
  { Environment~'#1'~not~defined~using~xparse. }
  {
    You~have~asked~for~the~argument~specification~for~an~environment~'#1',~
    but~this~is~not~an~environment~defined~using~xparse.
  }
\__msg_kernel_new:nnnn { xparse } { not-definable }
  { First~argument~of~'#2'~must~be~a~command. }
  {
    \c__msg_coding_error_text_tl
    The~first~argument~of~'#2'~should~be~the~document~command~that~will~
    be~defined.~The~provided~argument~'#1'~is~a~character.~Perhaps~a~
    backslash~is~missing?
    \\ \\
    LaTeX~will~ignore~this~entire~definition.
  }
\__msg_kernel_new:nnnn { xparse } { not-one-token }
  { First~argument~of~'#2'~must~be~a~command. }
  {
    \c__msg_coding_error_text_tl
    The~first~argument~of~'#2'~should~be~the~document~command~that~will~
    be~defined.~The~provided~argument~'#1'~contains~more~than~one~
    token.
    \\ \\
    LaTeX~will~ignore~this~entire~definition.
  }
\__msg_kernel_new:nnnn { xparse } { not-single-token }
  { Argument~delimiter~should~be~a~single~token:~'#1'. }
  {
    \c__msg_coding_error_text_tl
    The~argument~specification~provided~was~not~valid:~
    in~a~place~where~a~single~token~is~required,~LaTeX~found~'#1'. \\ \\
    LaTeX~will~ignore~this~entire~definition.
  }
\__msg_kernel_new:nnnn { xparse } { processor-in-expandable }
  { Argument~processors~cannot~be~used~with~expandable~functions. }
  {
    \c__msg_coding_error_text_tl
    The~argument~specification~for~#1~contains~a~processor~function:~
    this~is~only~supported~for~standard~robust~functions.
  }
\__msg_kernel_new:nnnn { xparse } { split-excess-tokens }
  { Too~many~'#1'~tokens~when~trying~to~split~argument. }
  {
    LaTeX~was~asked~to~split~the~input~'#3'~
    at~each~occurrence~of~the~token~'#1',~up~to~a~maximum~of~#2~parts.~
    There~were~too~many~'#1'~tokens.
  }
\__msg_kernel_new:nnnn { xparse } { unknown-argument-type }
  { Unknown~argument~type~'#1'~replaced~by~'m'. }
  {
    \c__msg_coding_error_text_tl
    The~letter~'#1'~does~not~specify~a~known~argument~type.~
    LaTeX~will~assume~you~want~a~standard~mandatory~argument~(type~'m').
  }
\__msg_kernel_new:nnnn { xparse } { unknown-command }
  { Unknown~document~command~'#1'. }
  {
    You~have~asked~for~the~argument~specification~for~a~command~'#1',~
    but~it~is~not~defined.
  }
\__msg_kernel_new:nnnn { xparse } { unknown-environment }
  { Unknown~document~environment~'#1'. }
  {
    You~have~asked~for~the~argument~specification~for~an~environment~'#1',~
    but~it~is~not~defined.
  }
\__msg_kernel_new:nnnn { xparse } { verbatim-newline }
  { Verbatim~argument~of~'#1'~ended~by~end~of~line. }
  {
    The~verbatim~argument~of~'#1'~cannot~contain~more~than~one~line,~
    but~the~end~
    of~the~current~line~has~been~reached.~You~have~probably~forgotten~the~
    closing~delimiter.
    \\ \\
    LaTeX~will~ignore~'#2'.
  }
\__msg_kernel_new:nnnn { xparse } { verbatim-tokenized }
  {
    The~verbatim~command~'#1'~cannot~be~used~inside~an~argument.~
  }
  {
    The~command~'#1'~takes~a~verbatim~argument.~
    It~may~not~appear~within~the~argument~of~another~function.~
    It~received~an~illegal~token \tl_if_empty:nF {#3} { ~'#3' } .
    \\ \\
    LaTeX~will~ignore~'#2'.
  }
%    \end{macrocode}
%
% Intended more for information.
%    \begin{macrocode}
\__msg_kernel_new:nnn { xparse } { define-command }
  {
    Defining~command~#1~
    with~sig.~'#2'~\msg_line_context:.
  }
\__msg_kernel_new:nnn { xparse } { define-environment }
  {
    Defining~environment~'#1'~
    with~sig.~'#2'~\msg_line_context:.
  }
\__msg_kernel_new:nnn { xparse } { redefine-command }
  {
    Redefining~command~#1~
    with~sig.~'#2'~\msg_line_context:.
  }
\__msg_kernel_new:nnn { xparse } { redefine-environment }
  {
    Redefining~environment~'#1'~
    with~sig.~'#2'~\msg_line_context:.
  }
%    \end{macrocode}
%
% \subsection{User functions}
%
% The user functions are more or less just the internal functions
% renamed.
%
% \begin{macro}{\BooleanFalse}
% \begin{macro}{\BooleanTrue}
%   Design-space names for the Boolean values.
%    \begin{macrocode}
\cs_new_eq:NN \BooleanFalse \c_false_bool
\cs_new_eq:NN \BooleanTrue  \c_true_bool
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\DeclareDocumentCommand}
% \begin{macro}{\NewDocumentCommand}
% \begin{macro}{\RenewDocumentCommand}
% \begin{macro}{\ProvideDocumentCommand}
%   The user macros are pretty simple wrappers around the internal ones.
%   There is however a check that the first argument is a single token
%   and is definable.
%    \begin{macrocode}
\cs_new_protected:Npn \DeclareDocumentCommand #1#2#3
  {
    \@@_check_definable:nNT {#1} \DeclareDocumentCommand
      { \@@_declare_cmd:Nnn #1 {#2} {#3} }
  }
\cs_new_protected:Npn \NewDocumentCommand #1#2#3
  {
    \@@_check_definable:nNT {#1} \NewDocumentCommand
      {
        \cs_if_exist:NTF #1
          {
            \__msg_kernel_error:nnx { xparse } { command-already-defined }
              { \token_to_str:N #1 }
          }
          { \@@_declare_cmd:Nnn #1 {#2} {#3} }
      }
  }
\cs_new_protected:Npn \RenewDocumentCommand #1#2#3
  {
    \@@_check_definable:nNT {#1} \RenewDocumentCommand
      {
        \cs_if_exist:NTF #1
          { \@@_declare_cmd:Nnn #1 {#2} {#3} }
          {
            \__msg_kernel_error:nnx { xparse } { command-not-yet-defined }
              { \token_to_str:N #1 }
          }
      }
  }
\cs_new_protected:Npn \ProvideDocumentCommand #1#2#3
  {
    \@@_check_definable:nNT {#1} \ProvideDocumentCommand
      { \cs_if_exist:NF #1 { \@@_declare_cmd:Nnn #1 {#2} {#3} } }
 }
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\DeclareDocumentEnvironment}
% \begin{macro}{\NewDocumentEnvironment}
% \begin{macro}{\RenewDocumentEnvironment}
% \begin{macro}{\ProvideDocumentEnvironment}
%   Very similar for environments.
%    \begin{macrocode}
\cs_new_protected:Npn \DeclareDocumentEnvironment #1#2#3#4
  { \@@_declare_env:nnnn {#1} {#2} {#3} {#4} }
\cs_new_protected:Npn \NewDocumentEnvironment #1#2#3#4
  {
    \cs_if_exist:cTF {#1}
      { \__msg_kernel_error:nnx { xparse } { environment-already-defined } {#1} }
      { \@@_declare_env:nnnn {#1} {#2} {#3} {#4} }
}
\cs_new_protected:Npn \RenewDocumentEnvironment #1#2#3#4
  {
    \cs_if_exist:cTF {#1}
      { \@@_declare_env:nnnn {#1} {#2} {#3} {#4} }
      { \__msg_kernel_error:nnx { xparse } { environment-not-yet-defined } {#1} }
  }
\cs_new_protected:Npn \ProvideDocumentEnvironment #1#2#3#4
  { \cs_if_exist:cF {#1} { \@@_declare_env:nnnn {#1} {#2} {#3} {#4} } }
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\DeclareExpandableDocumentCommand}
%   The expandable version of the basic function is essentially the same.
%    \begin{macrocode}
\cs_new_protected:Npn \DeclareExpandableDocumentCommand #1#2#3
  {
    \@@_check_definable:nNT {#1} \DeclareExpandableDocumentCommand
      { \@@_declare_expandable_cmd:Nnn #1 {#2} {#3} }
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[TF]{\IfBoolean}
%   The logical \meta{true} and \meta{false} statements are just the
%   normal \cs{c_true_bool} and \cs{c_false_bool}, so testing for them is
%   done with the \cs{bool_if:NTF} functions from \textsf{l3prg}.
%    \begin{macrocode}
\cs_new_eq:NN \IfBooleanTF \bool_if:NTF
\cs_new_eq:NN \IfBooleanT  \bool_if:NT
\cs_new_eq:NN \IfBooleanF  \bool_if:NF
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[TF]{\IfNoValue}
%   Simple re-naming.
%    \begin{macrocode}
\cs_new_eq:NN \IfNoValueF  \@@_if_no_value:nF
\cs_new_eq:NN \IfNoValueT  \@@_if_no_value:nT
\cs_new_eq:NN \IfNoValueTF \@@_if_no_value:nTF
%    \end{macrocode}
% \end{macro}
% \begin{macro}[TF]{\IfValue}
%   Inverted logic.
%    \begin{macrocode}
\cs_new_nopar:Npn \IfValueF { \@@_if_no_value:nT }
\cs_new_nopar:Npn \IfValueT { \@@_if_no_value:nF }
\cs_new:Npn \IfValueTF #1#2#3 { \@@_if_no_value:nTF {#1} {#3} {#2} }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\ProcessedArgument}
%   Processed arguments are returned using this name, which is reserved
%   here although the definition will change.
%    \begin{macrocode}
\tl_new:N \ProcessedArgument
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\ReverseBoolean, \SplitArgument, \SplitList, \TrimSpaces}
%   Simple copies.
%    \begin{macrocode}
\cs_new_eq:NN \ReverseBoolean \@@_bool_reverse:N
\cs_new_eq:NN \SplitArgument  \@@_split_argument:nnn
\cs_new_eq:NN \SplitList      \@@_split_list:nn
\cs_new_eq:NN \TrimSpaces     \@@_trim_spaces:n
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\ProcessList}
%   To support \cs{SplitList}.
%    \begin{macrocode}
\cs_new_eq:NN \ProcessList \tl_map_function:nN
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\GetDocumentCommandArgSpec}
% \begin{macro}{\GetDocumentEnvironmentArgSpec}
% \begin{macro}{\ShowDocumentCommandArgSpec}
% \begin{macro}{\ShowDocumentEnvironmentArgSpec}
%   More simple mappings, with a check that the argument is a single
%   control sequence or active character.
%    \begin{macrocode}
\cs_new_protected:Npn \GetDocumentCommandArgSpec #1
  {
    \@@_check_definable:nNT {#1} \GetDocumentCommandArgSpec
      { \@@_get_arg_spec:N #1 }
  }
\cs_new_eq:NN \GetDocumentEnvironmentArgSpec \@@_get_arg_spec:n
\cs_new_protected:Npn \ShowDocumentCommandArgSpec #1
  {
    \@@_check_definable:nNT {#1} \ShowDocumentCommandArgSpec
      { \@@_show_arg_spec:N #1 }
  }
\cs_new_eq:NN \ShowDocumentEnvironmentArgSpec \@@_show_arg_spec:n
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \subsection{Package options}
%
% \begin{variable}{\l_@@_options_clist}
% \begin{variable}{\l_@@_log_bool}
%   Key--value option to log information: done by hand to keep dependencies
%   down.
%    \begin{macrocode}
\clist_new:N \l_@@_options_clist
\DeclareOption* { \clist_put_right:NV \l_@@_options_clist \CurrentOption }
\ProcessOptions \relax
\keys_define:nn { xparse }
  {
    log-declarations .bool_set:N = \l_@@_log_bool ,
    log-declarations .initial:n  = true
  }
\keys_set:nV { xparse } \l_@@_options_clist
\bool_if:NF \l_@@_log_bool
  {
    \msg_redirect_module:nnn { LaTeX / xparse } { info }    { none }
    \msg_redirect_module:nnn { LaTeX / xparse } { warning } { none }
  }
%    \end{macrocode}
% \end{variable}
% \end{variable}
%
%    \begin{macrocode}
%</package>
%    \end{macrocode}
%
% \end{implementation}
%
% \PrintIndex