summaryrefslogtreecommitdiff
path: root/macros/luatex/generic/luaotfload/luaotfload-main.tex
blob: dbc8d73e7db2bb7f197acf8d909eece26905c445 (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
%% Copyright (C) 2009-2018
%%
%%      by  Elie Roux      <elie.roux@telecom-bretagne.eu>
%%      and Khaled Hosny   <khaledhosny@eglug.org>
%%      and Philipp Gesang <phg@phi-gamma.net>
%%
%% This file is part of Luaotfload.
%%
%%      Home:      https://github.com/lualatex/luaotfload
%%      Support:   <lualatex-dev@tug.org>.
%%
%% Luaotfload is under the GPL v2.0 (exactly) license.
%%
%% ----------------------------------------------------------------------------
%%
%% Luaotfload is free software; you can redistribute it and/or
%% modify it under the terms of the GNU General Public License
%% as published by the Free Software Foundation; version 2
%% of the License.
%%
%% Luaotfload is distributed in the hope that it will be useful,
%% but WITHOUT ANY WARRANTY; without even the implied warranty of
%% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
%% GNU General Public License for more details.
%%
%% You should have received a copy of the GNU General Public License
%% along with Luaotfload; if not, see <http://www.gnu.org/licenses/>.
%%
%% ----------------------------------------------------------------------------
%%

\beginfrontmatter

  \setdocumenttitle  {The \identifier{luaotfload} package}
  \setdocumentdate   {2019-11-04 v3.1}
  \setdocumentauthor {LaTeX3 Project\\
                      Elie Roux · Khaled Hosny · Philipp Gesang · Ulrike Fischer · Marcel Krüger\\
                      Home: \hyperlink {https://github.com/latex3/luaotfload}}

  \typesetdocumenttitle

  \beginabstractcontent
    This package is an adaptation of the \CONTEXT font loading system.
    It allows for loading \OpenType fonts with an extended syntax and adds
    support for a variety of font features.

    After discussion of the font loading API, this manual gives an
    overview of the core components of \identifier{Luaotfload}: The
    packaged font loader code, the names database, configuration, and
    helper functions on the \LUA\ end.
  \endabstractcontent

\endfrontmatter

\pdfbookmark[1]{\contentsname}{table}
\typesetcontent
\beginsection {Engine and version support}
\identifier{luaotfload} is a quite large and complex package. It imports code from context which is actively developed along with the luatex binary. It is not possible
to support a large number of engines variants or versions.

Supported is the \identifier{luatex} versions of a current TeXLive 2019 (and a current MiKTeX). Beginning with version 3.1 of this package also \identifier{luahbtex} is supported.
\endsection

\beginsection{Changes}
\beginsubsection {New in version 3.1 (by Ulrike Fischer/Marcel Krüger)}
\begin{itemize}
\item   The package has been moved to the github of the LaTeX3 Project and is now maintained
        officially by the LaTeX3 Project team.
\item   Code to use the harfbuzz library of luahbtex has been added. See the description of the harf mode.
\item   fonts in ttc-collections can now be indexed by name.    
\item   To reduce the polution of the global lua enviroment a number of lua tables have been removed.
        Only the tables \identifier{luaotfload}, \identifier{fonts} and \identifier{nodes} have been kept there.
\item   The fontloader has been synched with the context files from 2019-10-29.

\end{itemize}
\endsubsection


\beginsubsection {New in version 3.00 (by Ulrike Fischer/Marcel Krüger)}
\begin{itemize}
\item Default Ignorable characters are now invisible by default (issue 63). This can be deactivated with the option \texttt{invisible}.
\end{itemize}
\endsubsection

\beginsubsection {New in version 2.99 (by Ulrike Fischer)}
\begin{itemize}
\item Code cleanup.
\item The fontloader has been synched with the context files from 2019-08-11.
\end{itemize}
\endsubsection
\beginsubsection {New in version 2.98 (by Ulrike Fischer)}
\begin{itemize}
\item The\marginpar{\mbox{}\hfill \textbf{breaking change!}} handling of missing chars has been changed. In This version a missing char will insert the \inlinecode{/.notdef} char of the fonts (this is sometimes a space, sometimes a rectangle with a cross) and no longer simply ignore the glyph. This behaviour can be reverted by using \inlinecode{notdef=false} as font feature.
\item The font feature \inlinecode{embolden} can now be used to fake a bold font.
\item The fontloader has been synched with the context files from 2019-07-04.
\end{itemize}
\endsubsection
\beginsubsection {New in version 2.97 (by Ulrike Fischer)}
\begin{itemize}
\item the new generic fontloader improves the handling of large fonts (but some fonts still need a 64bit luatex version to create the font files).
\item A number of small bug (also in luaotfload-tool) have been corrected, see the NEWS file for details.

\end{itemize}
\endsubsection

\beginsubsection {New in version 2.96 (by Ulrike Fischer)}
\begin{itemize}
\item In\marginpar{\mbox{}\hfill \textbf{Incompatible change!}}
version 2.95 letterspacing was broken due to a change in the fontloader (issue 38). This has been repaired. At the same time a number of oddities and bugs in the letterspacing has been corrected. This can change existing documents. See page~\pageref{p:letterspace} for more information.

\item A problem with the detection of bold fonts has been corrected (issue 41, pull request 42).

\end{itemize}
\endsubsection



\beginsubsection {New in version 2.95 (by Ulrike Fischer)}
\begin{itemize}
\item
This version imports from context the generic fontloader in the version of 2019-01-28. Contrary to the last announcement, it still works with luatex 1.07. So updates will continue.

\item The handling of the lucida-fonts had been improved (issue 33).

\item tex-files are no longer misused as font fallbacks (issue 35).

\item The resolver code has be refactorated (pull request 36).

\end{itemize}
\endsubsection
\beginsubsection {New in version 2.94 (by Ulrike Fischer)}
\begin{itemize}
\item
This version imports from context the generic fontloader in the version of 2018-12-19. It is the last version that works with luatex 1.07 and texlive 2018. As context has moved to luatex 1.09 newer versions of the fontloader needs now this luatex version too. This means that until the texlive 2018 freeze there will be probably no update of luaotfload.

\item This version changes the handling of the \inlinecode{mode} key. It no longer accepts only the values \inlinecode{base} and \inlinecode{node}, but can be used to load a font with an alternative font loader/renderer.


\end{itemize}
\endsubsection

\beginsubsection {New in version 2.93 (by Ulrike Fischer)}
Mainly internal clean up of the version info to allow automatic versioning.
\endsubsection

\beginsubsection {New in version 2.92 (by Ulrike Fischer)}

\begin{itemize}

  \item Better devanagari support (issue \#9).
  \item \identifier{Luaotfload} doesn't work when luatex is used with the option \inlinecode{--safer}. So it now aborts cleanly when the option is detected -- but you still can get errors from fontspec later! (issue \#12).
  \item  The syntax \inlinecode{file:} for legacy font works again (issue \#11).
  \item The fontloader has been synched with the newest context version from october, 18.
\end{itemize}
\endsubsection
\beginsubsection {New in version 2.91 (by Ulrike Fischer)}

This version mostly correct two bugs found in the previous fontloader: Glyphvariants weren't copied and pasted correctly. Glyphs encoded in the PUA couldn't be accessed anymore.

\endsubsection


\beginsubsection {New in version 2.9 (by Ulrike Fischer)}

On the one side there is not very much new in this version: The native components of \identifier{Luaotfload} are nearly unchanged. A few bugs have been corrected, the various files lists which loads the components of the font loader have been cleaned up.

On the other side there is a lot new:

\begindescriptions

  \beginaltitem {Fontloader} The fontloader files imported from \CONTEXT\ have been updated to the current version.
   This was necessary to make \identifier{Luaotfload} compatible with the coming \LUATEX 1.08/1.09. Compared to the previous version from february 2017 quite a number of things have changed. Most importantly the handling of arabic fonts has greatly improved. But this also means that changes in the output are possible.
  \endaltitem

  \beginaltitem {Lualibs} The update of the fontloader files also required an update of the \identifier{Lualibs} package. This \identifier{Luaotfload} version needs version 2.6 of \identifier{Lualibs}.
  \endaltitem

  \beginaltitem {Maintenance} As the current maintainer wasn't available and it was urgent to get a \identifier{Luaotfload} compatible with \LUATEX 1.08/1.09 maintenance has been transfered to Ulrike Fischer and Marcel Krüger. The package was maintained and developed at \hyperlink{https://github.com/u-fischer/luaotfload}. Issues should be reported there.
  \endaltitem

  \beginaltitem {Documentation}
  The core of documentation is nearly unchanged. I added this introduction. I recreated with the help of @marmot the graphic on \pageref{file-graph}. I updated the file lists. I imported as appendix pdf versions of the two man files which are part of the \identifier{Luaotfload} documentation.
  \endaltitem

\enddescriptions

\endsubsection
\endsection
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\beginsection {Introduction}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Font management and installation has always been painful with \TEX.  A
lot of files are needed for one font (\abbrev{tfm}, \abbrev{pfb},
\abbrev{map}, \abbrev{fd}, \abbrev{vf}), and due to the 8-Bit encoding
each font is limited to 256 characters.

But the font world has evolved since the original \TEX, and new
typographic systems have appeared, most notably the so called
\emphasis{smart font} technologies like \OpenType fonts (\abbrev{otf}).

These fonts can contain many more characters than \TEX fonts, as well
as additional functionality like ligatures, old-style numbers, small
capitals, etc., and support more complex writing systems like Arabic
and Indic\footnote{%
  Unfortunately, the default fontloader of \identifier{luaotfload} doesn‘t support many Indic
  scripts correctly. For these scripts it is recommended to use the harf mode along with the binary \identifier{luahbtex}.}
scripts.

\OpenType fonts are widely deployed and available for all modern
operating systems.

As of 2013 they have become the de facto standard for advanced text
layout.

However, until recently the only way to use them directly in the \TEX
world was with the \XETEX engine.

Unlike \XETEX, \LUATEX has no built-in support for \OpenType or
technologies other than the original \TEX fonts.

Instead, it provides hooks for executing \LUA code during the \TEX run
that allow implementing extensions for loading fonts and manipulating
how input text is processed without modifying the underlying engine.

This is where \identifier{luaotfload} comes into play:
Based on code from \CONTEXT, it extends \LUATEX with functionality necessary
for handling \OpenType fonts.

Additionally, it provides means for accessing fonts known to the operating
system conveniently by indexing the metadata.

\endsection

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\beginsection {Thanks}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\identifier{Luaotfload} is part of \LUALATEX, the community-driven
project to provide a foundation for using the \LATEX format with the
full capabilites of the \LUATEX engine.
%
As such, the distinction between end users, contributors, and project
maintainers is intentionally kept less strict, lest we unduly
personalize the common effort.

Nevertheless, the current maintainers would like to express their
gratitude to Khaled Hosny, Akira Kakuto, Hironori Kitagawa and Dohyun
Kim.
%
Their contributions -- be it patches, advice, or systematic
testing -- made the switch from version 1.x to 2.2 possible.
%
Also, Hans Hagen, the author of the font loader, made porting the
code to \LATEX a breeze due to the extra effort he invested into
isolating it from the rest of \CONTEXT, not to mention his assistance
in the task and willingness to respond to our suggestions.

\endsection

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\beginsection {Loading Fonts}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\identifier{luaotfload} supports an extended font request syntax:

\beginnarrower
      \nonproportional{\string\font\string\foo\space= \string{}%
      \meta{prefix}\nonproportional{:}%
      \meta{font name}\nonproportional{:}%
      \meta{font features}\nonproportional{\string}}%
      \meta{\TEX font features}
\endnarrower

\noindent
The curly brackets are optional and escape the spaces in the enclosed
font name.
%
Alternatively, double quotes serve the same purpose.
%
A selection of individual parts of the syntax are discussed below;
for a more formal description see figure \ref{font-syntax}.

\beginsyntaxfloat
  {font-syntax}
  {Font request syntax.
   Braces or double quotes around the
   \emphasis{specification} rule will
   preserve whitespace in file names.
   In addition to the font style modifiers
   (\emphasis{slash-notation}) given above, there
   are others that are recognized but will be silently
   ignored: \nonproportional{aat},
            \nonproportional{icu}, and
            \nonproportional{gr}.
   The special terminals are:
   \smallcaps {feature\textunderscore id} for a valid font
      feature name and
   \smallcaps {feature\textunderscore value} for the corresponding
      value.
   \smallcaps {tfmname} is the name of a \abbrev{tfm} file.
   \smallcaps {digit}  again refers to bytes 48--57, and
   \smallcaps {all\textunderscore characters} to all byte values.
   \smallcaps {csname} and \smallcaps {dimension} are the \TEX concepts.}
%
      <definition>      ::= `\\font', {\sc csname}, `=', <font request>, [ <size> ] ;

      <size>            ::= `at', {\sc dimension} ;

      <font request>    ::= `"', <unquoted font request> `"'
      \alt                  `{', <unquoted font request> `}'
      \alt                  <unquoted font request> ;

      <unquoted font request> ::= <specification>, [`:', <feature list> ]
      \alt                        <path lookup>, [ [`:'], <feature list> ] ;

      <specification>    ::= <prefixed spec>, [ <subfont no> ], \{ <modifier> \}
      \alt                   <anon lookup>, \{ <modifier> \} ;

      <prefixed spec>    ::= `combo:', <combo list>
      \alt                   `file:', <file lookup>
      \alt                   `name:', <name lookup> ;

      <combo list>       ::= <combo def 1>, \{ `;', <combo def>  \} ;

      <combo def 1>      ::= <combo id>, `->', <combo id> ;

      <combo def>        ::= <combo id>, `->', <combo id chars> ;

      <combo id>         ::= (`(', \{ {\sc digit} \}, `)' | \{ {\sc digit} \} ) ;

      <combo id chars>   ::= (`(', \{ {\sc digit} \}, `,', <combo chars>, `)'
      \alt                   \{ {\sc digit} \} ) ;

      <combo chars>      ::= `fallback'
      \alt                   \{ <combo range>, \{ `*', <combo range> \} \} ;

      <combo range>      ::= <combo num>, [ `-', <combo num> ] ;

      <combo num>        ::= `0x', \{ {\sc hexdigit}  \}
      \alt                   `U+', \{ {\sc digit} \}
      \alt                   \{ {\sc digit} \} ;

      <file lookup>      ::= \{ <name character> \} ;

      <name lookup>      ::= \{ <name character> \} ;

      <anon lookup>      ::= {\sc tfmname} | <name lookup> ;

      <path lookup>      ::= `[', \{ <path content> \}, `]', [ <subfont no> ] ;

      <path content>     ::= <path balanced>
      \alt                   `\\', {\sc all_characters}
      \alt                   {\sc all_characters} - `]'

      <path balanced>    ::= `[', [ <path content> ], `]'

      <modifier>         ::= `/', (`I' | `B' | `BI' | `IB' | `S=', \{ {\sc digit} \} ) ;

      <subfont no>       ::= `(', \{ {\sc digit} \}, `)' ;

      <feature list>     ::= <feature expr>, \{ `;', <feature expr> \} ;

      <feature expr>     ::= {\sc feature_id}, `=', {\sc feature_value}
      \alt                   <feature switch>, {\sc feature_id} ;

      <feature switch>   ::= `+' | `-' ;

      <name character>   ::= {\sc all_characters} - ( `(' | `/' | `:' ) ;
\endsyntaxfloat

%% Below guarded space gets borked in index; why‽
\beginsubsection{Prefix -- the \texorpdfstring{\identifier{luaotfload}}{luaotfload}{ }Way}

In \identifier{luaotfload}, the canonical syntax for font requests
requires a \emphasis{prefix}:
%
\beginnarrower
  \nonproportional{\string\font\string\fontname\space= }%
  \meta{prefix}%
  \nonproportional{:}%
  \meta{fontname}%
  \dots
\endnarrower
%
where \meta{prefix} is either \inlinecode{file:} or \inlinecode {name:}.\footnote{%
  \identifier{Luaotfload} also knows two further prefixes, \inlinecode {kpse:}
  and \inlinecode {my:}.
  %
  A \inlinecode {kpse} lookup is restricted to files that can be found by
  \identifier{kpathsea} and will not attempt to locate system fonts.
  %
  This behavior can be of value when an extra degree of encapsulation is
  needed, for instance when supplying a customized tex distribution.

  The \inlinecode {my} lookup takes this a step further: it lets you define
  a custom resolver function and hook it into the \luaident{resolve_font}
  callback.
  %
  This ensures full control over how a file is located.
  %
  For a working example see the
  \hyperlink [test in the luaotfload
  repo]{https://github.com/latex3/luaotfload/blob/master/testfiles/my-resolver.lvt}.
}
%
It determines whether the font loader should interpret the request as
a \emphasis{file name} or
  \emphasis{font name}, respectively,
which again influences how it will attempt to locate the font.
%
Examples for font names are
            “Latin Modern Italic”,
            “GFS Bodoni Rg”, and
            “PT Serif Caption”
-- they are the human readable identifiers
usually listed in drop-down menus and the like.\footnote{%
  Font names may appear like a great choice at first because they
  offer seemingly more intuitive identifiers in comparison to arguably
  cryptic file names:
  %
  “PT Sans Bold” is a lot more descriptive than \fileent{PTS75F.ttf}.
  On the other hand, font names are quite arbitrary and there is no
  universal method to determine their meaning.
  %
  While \identifier{luaotfload} provides fairly sophisticated heuristic
  to figure out a matching font style, weight, and optical size, it
  cannot be relied upon to work satisfactorily for all font files.
  %
  For an in-depth analysis of the situation and how broken font names
  are, please refer to
  \hyperlink [this post]{http://www.ntg.nl/pipermail/ntg-context/2013/073889.html}
  by Hans Hagen, the author of the font loader.
  %
  If in doubt, use filenames.
  %
  \fileent{luaotfload-tool} can perform the matching for you with the
  option \inlinecode {--find=<name>}, and you can use the file name it returns
  in your font definition.
}
%
In order for fonts installed both in system locations and in your
\fileent{texmf} to be accessible by font name, \identifier{luaotfload} must
first collect the metadata included in the files.
%
Please refer to section~\ref{sec:fontdb} below for instructions on how to
create the database.

File names are whatever your file system allows them to be, except
that that they may not contain the characters
  \inlinecode {(},
  \inlinecode {:}, and
  \inlinecode {/}.
%
As is obvious from the last exception, the \inlinecode {file:} lookup will
not process paths to the font location -- only those
files found when generating the database are addressable this way.
%
Continue below in the \XETEX section if you need to load your fonts
by path.
%
The file names corresponding to the example font names above are
  \fileent{lmroman12-italic.otf},
  \fileent{GFSBodoni.otf}, and
  \fileent{PTZ56F.ttf}.

\endsubsection

\beginsubsection {Bracketed Lookups}
\label{sec:bracket}
Bracketed lookups allow for arbitrary character content to be used in a
definition.
%
A simple bracketed request looks follows the scheme

\beginnarrower
  \nonproportional{\string\font\string\fontname\space = [}%
  \meta{/path/to/file}%
  \nonproportional{]}
\endnarrower

\noindent
Inside the square brackets, every character except for a closing bracket is
permitted, allowing for  arbitrary paths to a font file -- including Windows
style paths with UNC or drive letter prepended -- to be specified.
%
The \identifier{Luaotfload} syntax differs from \XETEX in that the subfont
selector goes \emphasis{after} the closing bracket:

\beginnarrower
  \nonproportional{\string\font\string\fontname\space = [}%
  \meta{/path/to/file}%
  \nonproportional{]}
  \nonproportional{(}n\nonproportional{)}
\endnarrower

Naturally, path-less file names are equally valid and processed the
same way as an ordinary \inlinecode {file:} lookup.

\beginsubsection {Compatibility}

In addition to the regular prefixed requests, \identifier{luaotfload}
accepts loading fonts the \XETEX way.
%
There are again two modes: bracketed and unbracketed.
For the bracketed variety, see above, \ref{sec:bracket}.

Unbracketed (or, for lack of a better word: \emphasis{anonymous})
font requests resemble the conventional \TEX syntax.

\beginnarrower
  \nonproportional{\string\font\string\fontname\space= }%
  \meta{font name}
  \dots
\endnarrower
\endsubsection

However, they have a broader spectrum of possible interpretations:
before anything else, \identifier{luaotfload} attempts to load a
traditional \TEX Font Metric (\abbrev{tfm} or \abbrev{ofm}).
%
If this fails, it performs a \inlinecode {path:} lookup, which itself will
fall back to a \inlinecode {file:} lookup.
%
Lastly, if none of the above succeeded, attempt to resolve the request as a
\inlinecode {name:} lookup by searching the font index for \meta{font name}.
%
The behavior of this “anonymous” lookup is configurable, see the configuation
manpage for details.

Furthermore, \identifier{luaotfload} supports the slashed (shorthand)
font style notation from \XETEX.

\beginnarrower
  \nonproportional{\string\font\string\fontname\space= }%
  \meta{font name}%
  \nonproportional{/}%
  \meta{modifier}
  \dots
\endnarrower

\noindent
Currently, four style modifiers are supported:
  \inlinecode {I} for italic shape,
  \inlinecode {B} for bold   weight,
  \inlinecode {BI} or \inlinecode {IB} for the combination of both.
%
Other “slashed” modifiers are too specific to the \XETEX engine and
have no meaning in \LUATEX.

\endsubsection

\beginsubsection{Examples}

\beginsubsubsection{Loading by File Name}

For example, conventional \TeX\ font can be loaded with a
\inlinecode {file:} request like so:

\beginlisting
  \font \lmromanten = {file:ec-lmr10} at 10pt
\endlisting

The \OpenType version of Janusz Nowacki’s font \emphasis{Antykwa
Półtawskiego}\footnote{%
  \hyperlink {http://jmn.pl/antykwa-poltawskiego/}, also available in
  in \TEX Live.
}
in its condensed variant can be loaded as follows:

\beginlisting
  \font \apcregular = file:antpoltltcond-regular.otf at 42pt
\endlisting

The next example shows how to load the \emphasis{Porson} font digitized by
the Greek Font Society using \XETEX-style syntax and an absolute path from a
non-standard directory:

\beginlisting
  \font \gfsporson = "[/tmp/GFSPorson.otf]" at 12pt
\endlisting

\identifier{TrueType} collection files (the extension is usually
\inlinecode{.ttc}) contain more than a single font. In order to refer to these
subfonts, the respective index or the respective PostScript font name may be
added in parentheses after the file name.\footnote{%
  Incidentally, this syntactical detail also prevents one from loading files
  that end in balanced parentheses.
}

\beginlisting
  \font \cambriamain = "file:cambria.ttc(0)" at 10pt
  \font \cambriamath = "file:cambria.ttc(1)" at 10pt
  \font \Cambriamain = "file:cambria.ttc(Cambria)" at 10pt
  \font \Cambriamath = "file:cambria.ttc(CambriaMath)" at 10pt
\endlisting

and likewise, requesting subfont inside a TTC container by path:

\beginlisting
  \font \asanamain = "[/home/typesetter/.fonts/math/asana.ttc](0):mode=node;+tlig" at 10pt
  \font \asanamath = "[/home/typesetter/.fonts/math/asana.ttc](1):mode=base" at 10pt
\endlisting

\endsubsubsection

\beginsubsubsection{Loading by Font Name}

The \inlinecode {name:} lookup does not depend on cryptic filenames:

\beginlisting
  \font \pagellaregular = {name:TeX Gyre Pagella} at 9pt
\endlisting

A bit more specific but essentially the same lookup would be:

\beginlisting
  \font \pagellaregular = {name:TeX Gyre Pagella Regular} at 9pt
\endlisting

\noindent
Which fits nicely with the whole set:

\beginlisting
  \font\pagellaregular    = {name:TeX Gyre Pagella Regular}    at 9pt
  \font\pagellaitalic     = {name:TeX Gyre Pagella Italic}     at 9pt
  \font\pagellabold       = {name:TeX Gyre Pagella Bold}       at 9pt
  \font\pagellabolditalic = {name:TeX Gyre Pagella Bolditalic} at 9pt

  {\pagellaregular     foo bar baz\endgraf}
  {\pagellaitalic      foo bar baz\endgraf}
  {\pagellabold        foo bar baz\endgraf}
  {\pagellabolditalic  foo bar baz\endgraf}

  ...
\endlisting

\endsubsubsection

\beginsubsubsection{Modifiers}

If the entire \emphasis{Iwona} family\footnote{%
  \hyperlink {http://jmn.pl/kurier-i-iwona/},
  also in \TEX Live.
}
is installed in some location accessible by \identifier{luaotfload},
the regular shape can be loaded as follows:

\beginlisting
  \font \iwona = Iwona at 20pt
\endlisting

\noindent
To load the most common of the other styles, the slash notation can
be employed as shorthand:

\beginlisting
  \font \iwonaitalic     = Iwona/I    at 20pt
  \font \iwonabold       = Iwona/B    at 20pt
  \font \iwonabolditalic = Iwona/BI   at 20pt
\endlisting

\noindent
which is equivalent to these full names:

\beginlisting
  \font \iwonaitalic     = "Iwona Italic"       at 20pt
  \font \iwonabold       = "Iwona Bold"         at 20pt
  \font \iwonabolditalic = "Iwona BoldItalic"   at 20pt
\endlisting

\endsubsubsection
\endsubsection
\endsection

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\beginsection {Font features}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\emphasis{Font features} are the second to last component in the
general scheme for font requests:

\beginnarrower
  \nonproportional{\string\font\string\foo\space= "}%
  \meta{prefix}%
  \nonproportional{:}%
  \meta{font name}%
  \nonproportional{:}%
  \meta{font features}%
  \meta{\TEX font features}%
  \nonproportional{"}
\endnarrower

\noindent
If style modifiers are present (\XETEX style), they must precede
\meta{font features}.

The element \meta{font features} is a semicolon-separated list of feature
tags\footnote{%
  Cf. \hyperlink {http://www.microsoft.com/typography/otspec/featurelist.htm}.
}
and font options.
%
Prepending a font feature with a \inlinecode{+} (plus sign) enables it,
whereas a \inlinecode{-} (minus) disables it. For instance, the request

\beginlisting
  \font \test = LatinModernRoman:+clig;-kern
\endlisting

\noindent activates contextual ligatures (\inlinecode{clig}) and
disables kerning (\inlinecode{kern}).
%
Alternatively the options \inlinecode{true} or \inlinecode{false} can
be passed to the feature in a key/value expression.
%
The following request has the same meaning as the last one:

\beginlisting
  \font \test = LatinModernRoman:clig=true;kern=false
\endlisting

\noindent
Furthermore, this second syntax is required should a font feature
accept other options besides a true/false switch.
%
For example, \emphasis{stylistic alternates} (\inlinecode{salt}) are
variants of given glyphs.
%
They can be selected either explicitly by supplying the variant
index (starting from one), or randomly by setting the value to,
obviously, \inlinecode{random}.

%% TODO   verify that this actually works with a font that supports
%%        the salt/random feature!\fi
\beginlisting
  \font \librmsaltfirst = LatinModernRoman:salt=1
\endlisting

\beginsubsection {Basic font features}\label{sec:mode}

\begindescriptions

  \beginaltitem {mode}
         \identifier{luaotfload} had three \OpenType processing
         \emphasis{modes}:
         \identifier{base}, \identifier{node} and \identifier{harf}.

         \identifier{base} mode works by mapping \OpenType
         features to traditional \TEX ligature and kerning mechanisms.
         %
         Supporting only non-contextual substitutions and kerning
         pairs, it is the slightly faster, albeit somewhat limited, variant.
         %
         \identifier{node} mode works by processing \TeX’s internal
         node list directly at the \LUA end and supports
         a wider range of \OpenType features.
         %
         The downside is that the intricate operations required for
         \identifier{node} mode may slow down typesetting especially
         with complex fonts and it does not work in math mode.

         By default \identifier{luaotfload} is in \identifier{node}
         mode, and \identifier{base} mode has to be requested where needed,
         e.~g. for math fonts.

         \identifier{harf} mode is new in version 3.1 and needs the new \identifier{luahbtex} engine (the mode is ignored if \identifier{luahbtex} is not used). With it is possible to render a font using the harfbuzz library in-built in the new engine. \identifier{harf} mode improves greatly the rendering of indic and arabic scripts and is highly recommended for such scripts.

         When using \identifier{harf} mode it is required to set also the script correctly:


         \beginlisting
         \font\burmesefont={file:NotoSerifMyanmar-Regular.ttf:mode=harf;script=mymr;}
         \font\devafont={file:NotoSansDevanagari-Regular.ttf:mode=harf;script=deva;}
         \font\banglafont={name:Noto Sans Bengali:mode=harf;script=beng;}
         \font\tibetanfont={name:Noto Serif Tibetan:mode=harf;script=tibt;}
         \endlisting

         \includegraphics{scripts-demo}


         It is possible to call other font renderers with the mode key. A simple example with a plain reader can be found at \url{https://github.com/latex3/luaotfload/pull/26#issuecomment-437716326}.

  \endaltitem
  \beginaltitem {shaper} \label{shaper-tag}
  If \identifier{luahbtex} and \identifier{harf} mode are used it is possible to specify a shaper, like \identifier{graphite2} or \identifier{ot} (open type).

  \beginlisting
  \pardir TRT\textdir TRT
  \font\test={file:AwamiNastaliq-Regular.ttf:mode=harf;shaper=ot}
  \endlisting

  \includegraphics{shaper-demo}

  \beginlisting
  \pardir TRT\textdir TRT
  \font\test={file:AwamiNastaliq-Regular.ttf:mode=harf;shaper=graphite2}
  \endlisting

  \includegraphics{shaper-demo-graphite}

  \endaltitem
  \beginaltitem {script} \label{script-tag}
         An \OpenType script tag;\footnote{%
           See \hyperlink {http://www.microsoft.com/typography/otspec/scripttags.htm}
           for a list of valid values.
           %
           For scripts derived from the Latin alphabet the value
           \inlinecode{latn} is good choice.
         }
         the default value is \inlinecode{dflt}.
         %
         Some fonts, including very popular ones by foundries like Adobe,
         do not assign features to the \inlinecode{dflt} script, in
         which case the script needs to be set explicitly.
  \endaltitem

  \beginaltitem {language}
         An \OpenType language system identifier,\footnote{%
           Cf. \hyperlink {http://www.microsoft.com/typography/otspec/languagetags.htm}.
         }
         defaulting to \inlinecode{dflt}.
  \endaltitem

  \beginaltitem {color}
         A font color, defined as a triplet of two-digit hexadecimal
         \abbrev{rgb} values, with an optional fourth value for
         transparency
         (where \inlinecode{00} is completely transparent and
         \inlinecode{FF} is opaque).

         For example, in order to set text in semitransparent red:

         \beginlisting
      \font \test = "Latin Modern Roman:color=FF0000BB"
         \endlisting
  \endaltitem


   \beginaltitem {embolden}
         A factor, defined as a decimal number.

         For example

         \beginlisting
      \font\test = "Latin Modern Roman:mode=node;embolden=2;"
         \endlisting

      {\font\test= "Latin Modern Roman:mode=node;"\test Dies is not bold.
       \font\test= "Latin Modern Roman:mode=node;embolden=2;" \test Dies is a faked bold font.}

  \endaltitem

  \beginaltitem {kernfactor \& letterspace}\label{p:letterspace}
         Define a font with letterspacing (tracking) enabled.
         %
         In \identifier{luaotfload}, letterspacing is implemented by
         inserting additional kerning between glyphs.

         This approach is derived from and still quite similar to the
         \emphasis{character kerning} (\texmacro{setcharacterkerning} /
         \texmacro{definecharacterkerning} \& al.) functionality of
         Context, see the file \fileent{typo-krn.lua} there.
         %
         The main difference is that \identifier{luaotfload} does not
         use \LUATEX attributes to assign letterspacing to regions,
         but defines virtual letterspaced versions of a font.

         The option \identifier{kernfactor} accepts a numeric value that
         determines the letterspacing factor to be applied to the font
         size.
         %
         E.~g. a kern factor of $0.42$ applied to a $10$ pt font
         results in $4.2$ pt of additional kerning applied to each
         pair of glyphs.
         %

         Spaces\marginpar{\mbox{}\hfill NEW in v2.96!} between words are now stretched too. This is consistent with the \XETEX behaviour (and the amount of stretching should be similar). This
         naturally changes the output of a document.  In case you want the old behaviour back use
         \beginlisting
           \directlua{luaotfload.letterspace.keepwordspacing = true}
         \endlisting

         The difference between both options is obvious:

         \begingroup
         \fontspec{IwonaMedium-Regular.otf}[LetterSpace=60]
          New: hello world

          \directlua{luaotfload.letterspace.keepwordspacing = true}

          Old: hello world

          \directlua{luaotfload.letterspace.keepwordspacing = false}
          \endgroup


         Ligatures\marginpar{\mbox{}\hfill NEW in v2.96!}  are no longer split into their component glyphs.
         This change too make the \identifier{luaotfload} more compatible with \XETEX. It also makes it much easier to activate or deactivate ligature sets in letterspaced fonts.
         If you want to split ligatures, you should deactivate as you would do it with a not-letterspaced font, e.g. with the fontspec \identifier{Ligatures} option, or the low-level \identifier{-liga} and similar.


         {\font \test = "file:Iwona-Regular.otf:mode=base;+liga;+tlig;letterspace=12.5"
          \test With standard ligatures: fi -- ff\par

          \font \test = "file:Iwona-Regular.otf:mode=base;-liga;+tlig;letterspace=12.5"
          \test Only with tlig: fi -- ff \par

          \font \test = "file:Iwona-Regular.otf:mode=base;-liga;letterspace=12.5"
          \test No ligatures: fi -- ff \par
         }

         For compatibility with \XETEX an alternative
         \identifier{letterspace} option is supplied that interprets the
         supplied value as a \emphasis{percentage} of the font size but
         is otherwise identical to \identifier{kernfactor}.
         %
         Consequently, both definitions in below snippet yield the same
         letterspacing width:

         \beginlisting
    \font \iwonakernedA = "file:Iwona-Regular.otf:kernfactor=0.125"
    \font \iwonakernedB = "file:Iwona-Regular.otf:letterspace=12.5"
         \endlisting

         The \identifier{microtype} package uses a special implementation of letterspacing, and the commands \inlinecode{\lsstyle} and \inlinecode{\textls} are  not affected by these changes.

         Setting the ligatures with the font options is the recommended way, to activate or deactivate them. In case of special requirements
         specific pairs of letters and ligatures may be exempt from
         letterspacing by defining the \LUA functions
         \luaident{keeptogether} and \luaident{keepligature},
         respectively, inside the namespace \inlinecode {luaotfload.letterspace}.
         %
         Both functions are called whenever the letterspacing callback
         encounters an appropriate node or set of nodes.
         %
         If they return a true-ish value, no extra kern is inserted at
         the current position.
         %
         \luaident{keeptogether} receives a pair of consecutive
         glyph nodes in order of their appearance in the node list.
         %
         \luaident{keepligature} receives a single node which can be
         analyzed into components.
         %
         (For details refer to the \emphasis{glyph nodes} section in the
         \LUATEX reference manual.)
         %
         The implementation of both functions is left entirely to the
         user.
  \endaltitem

\iffalse
  \startbuffer [printvectors]
  \directlua{inspect(fonts.protrusions.setups.default)
             inspect(fonts.expansions.setups.default)}
  \stopbuffer
\fi

  \beginaltitem {protrusion \& expansion}
         These keys control microtypographic features of the font,
         namely \emphasis{character protrusion} and \emphasis{font
         expansion}.
         %
         Their arguments are names of \LUA tables that contain
         values for the respective features.\footnote{%
            For examples of the table layout please refer to the
            section of the file \fileent{luaotfload-fonts-ext.lua} where the
            default values are defined.
            %
            Alternatively and with loss of information, you can dump
            those tables into your terminal by issuing
            \unless \iffalse
              \beginlisting
 \directlua{inspect(fonts.protrusions.setups.default)
            inspect(fonts.expansions.setups.default)}
              \endlisting
            \else
              \typebuffer [printvectors]
            \fi
            at some point after loading \fileent{luaotfload.sty}.
         }
         %
         For both, only the set \identifier{default} is predefined.

         For example, to define a font with the default
         protrusion vector applied\footnote{%
           You also need to set
               \inlinecode {pdfprotrudechars=2} and
               \inlinecode {pdfadjustspacing=2}
           to activate protrusion and expansion, respectively.
           See the
           \hyperlink [\PDFTEX manual]{http://mirrors.ctan.org/systems/pdftex/manual/pdftex-a.pdf}%
           for details.
         }:

         \beginlisting
      \font \test = LatinModernRoman:protrusion=default
         \endlisting
  \endaltitem

 \beginaltitem {invisible}
         Default Ignorable characters are control characters that should be invisible by default even if the font has glyphs for them. Since version 3.0 luaotfload makes them invisible, this can be switch on and off with the \texttt{invisible}. By default it is on.

         For example

         \beginlisting
         \font\amiri={file:amiri-regular.ttf} at 20pt \amiri
         \char"200Dي\char"200D
         \endlisting

       {\font\amiri={file:amiri-regular.ttf} at 20pt \amiri \char"200Dي\char"200D}

    \beginlisting
         \font\amiri={file:amiri-regular.ttf:-invisible;} at 20pt \amiri
         \char"200Dي\char"200D
         \endlisting

       {\font\amiri={file:amiri-regular.ttf:-invisible;} at 20pt \amiri \char"200Dي\char"200D}


  \endaltitem
\enddescriptions

\endsubsection

\beginsubsection {Non-standard font features}
\identifier{luaotfload} adds a number of features that are not defined
in the original \OpenType specification, most of them
aiming at emulating the behavior familiar from other \TEX engines.
%
Currently (2014) there are three of them:

\begindescriptions

  \beginaltitem {anum}
          Substitutes the glyphs in the \abbrev{ascii} number range
          with their counterparts from eastern Arabic or Persian,
          depending on the value of \identifier{language}.
  \endaltitem

  \beginaltitem {tlig}
          Applies legacy \TEX ligatures\footnote{%
            These contain the feature set \inlinecode {trep} of earlier
            versions of \identifier{luaotfload}.

            Note to \XETEX users: this is the equivalent of the
            assignment \inlinecode {mapping=text-tex} using \XETEX's input
            remapping feature.
          }:

          \unless \iffalse
            %% Using braced arg syntax with inline code appears to be
            %% impossible within Latex tables -- just ignore the weird
            %% exclamation points below.
            \begintabulate [rlrl]
              \beginrow ``  \newcell  {\inlinecode !``! } \newcell  ''  \newcell  {\inlinecode !''!} \endrow
              \beginrow `   \newcell  {\inlinecode !`!  } \newcell  '   \newcell  {\inlinecode !'! } \endrow
              \beginrow "   \newcell  {\inlinecode !"!  } \newcell  --  \newcell  {\inlinecode !--!} \endrow
              \beginrow --- \newcell  {\inlinecode !---!} \newcell  !`  \newcell  {\inlinecode ?!`?} \endrow
              \beginrow ?`  \newcell  {\inlinecode !?`! } \newcell      \newcell                     \endrow
            \endtabulate
          \else
            %% XXX find a way to wrap these in the tabulate environment
            \startframed [frame=off,width=broad,align=middle]
              \startframed [frame=off,width=\dimexpr(\textwidth/2)]
                \startxtable [align=middle]
                    \startxrow \startxcell ``  \stopxcell \startxcell  \inlinecode {``}  \stopxcell \startxcell  ''  \stopxcell \startxcell  \inlinecode {''}  \stopxcell \stopxrow
                    \startxrow \startxcell `   \stopxcell \startxcell  \inlinecode {`}   \stopxcell \startxcell  '   \stopxcell \startxcell  \inlinecode {'}   \stopxcell \stopxrow
                    \startxrow \startxcell "   \stopxcell \startxcell  \inlinecode {"}   \stopxcell \startxcell  --  \stopxcell \startxcell  \inlinecode {--}  \stopxcell \stopxrow
                    \startxrow \startxcell --- \stopxcell \startxcell  \inlinecode {---} \stopxcell \startxcell  !`  \stopxcell \startxcell  \inlinecode {!`}  \stopxcell \stopxrow
                    \startxrow \startxcell ?`  \stopxcell \startxcell  \inlinecode {?`}  \stopxcell \startxcell      \stopxcell \startxcell                    \stopxcell \stopxrow
                \stopxtable
              \stopframed
            \stopframed
          \fi
  \endaltitem

  \beginaltitem {itlc}
          Computes italic correction values (active by default).
  \endaltitem

\enddescriptions

\endsubsection
\endsection

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\beginsection {Combining fonts}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Version 2.7 and later support combining characters from multiple fonts into a
single virtualized one. This requires that the affected fonts be loaded in
advance as well as a special \emphasis{request syntax}. Furthermore, this
allows to define \emphasis{fallback fonts} to supplement fonts that may lack
certain required glyphs.

Combinations are created by defining a font using the \luaident{combo:} prefix.

\beginsubsection {Fallbacks}

For example, the \identifier{Latin Modern} family of fonts does, as indicated
in the name, not provide Cyrillic glyphs. If Latin script dominates in the copy
with interspersed Cyrillic, a fallback can be created from a similiar looking
font like \identifier{Computer Modern Unicode}, taking advantage of the fact
that it too derives from Knuth’s original \identifier{Computer Modern} series:

\beginlisting
  \input luaotfload.sty
  \font \lm  = file:lmroman10-regular.otf:mode=base
  \font \cmu = file:cmunrm.otf:mode=base
  \font \lmu = "combo: 1->\fontid\lm; 2->\fontid\cmu,fallback"
  \lmu Eh bien, mon prince. Gênes et Lueques ne sont plus que des
       apanages, des поместья, de la famille Buonaparte.
  \bye
\endlisting

As simple as this may look on the first glance, this approach is entirely
inappropriate if more than a couple letters are required from a different font.
Because the combination pulls nothing except the glyph data, all of the
important other information that constitute a proper font -- kerning, styles,
features, and suchlike -- will be missing.

\endsubsection %% Fallbacks

\beginsubsection {Combinations}

Generalizing the idea of a \emphasis{fallback font}, it is also possible to
pick definite sets of glyphs from multiple fonts. On a bad day, for instance,
it may be the sanest choice to start out with \identifier{EB Garamond} italics,
typeset all decimal digits in the bold italics of \identifier{GNU Freefont},
and tone down the punctuation with extra thin glyphs from \identifier{Source
Sans}:

\beginlisting
  \def \feats     {-tlig;-liga;mode=base;-kern}
  \def \fileone   {EBGaramond12-Italic.otf}
  \def \filetwo   {FreeMonoBoldOblique.otf}
  \def \filethree {SourceSansPro-ExtraLight.otf}

  \input luaotfload.sty

  \font \one   = file:\fileone  :\feats
  \font \two   = file:\filetwo  :\feats
  \font \three = file:\filethree:\feats

  \font \onetwothree = "combo:  1 -> \fontid\one;
                                2 -> \fontid\two,   0x30-0x39;
                                3 -> \fontid\three, 0x21*0x3f; "

  {\onetwothree \TeX—0123456789—?!}
  \bye
\endlisting

\noindent Despite the atrocious result, the example demonstrates well the
syntax that is used to specify ranges and fonts. Fonts are being referred to by
their internal index which can be obtained by passing the font command into the
\texmacro{fontid} macro, e. g. \inlinecode{\fontid\one}, after a font has been
defined. The first component of the combination is the base font which will be
extended by the others. It is specified by the index alone.

All further fonts require either the literal \inlinecode{fallback} or a list of
codepoint definitions to be appended after a comma. The elements of this list
again denote either single codepoints like \inlinecode{0x21} (referring to the
exclamation point character) or ranges of codepoints (\inlinecode{0x30-0x39}).
Elements are separated by the \identifier{ASCII} asterisk character
(\inlinecode{*}). The characters referenced in the list will be imported from
the respective font, if available.

\endsubsection %% Combinations

\endsection

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\beginsection {Font names database}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\label{sec:fontdb}

As mentioned above, \identifier{luaotfload} keeps track of which
fonts are available to \LUATEX by means of a \emphasis{database}.
%
This allows referring to fonts not only by explicit filenames but
also by the proper names contained in the metadata which is often
more accessible to humans.\footnote{%
  The tool \hyperlink[\fileent{otfinfo}]{http://www.lcdf.org/type/}
  (comes with \TEX Live), when invoked on a font file with the
  \inlinecode {-i} option, lists the variety of name fields defined for
  it.
}

When \identifier{luaotfload} is asked to load a font by a font name,
it will check if the database exists and load it, or else generate a
fresh one.
%
Should it then fail to locate the font, an update to the database is
performed in case the font has been added to the system only
recently.
%
As soon as the database is updated, the resolver will try
and look up the font again, all without user intervention.
%
The goal is for \identifier{luaotfload} to act in the background and
behave as unobtrusively as possible, while providing a convenient
interface to the fonts installed on the system.

Generating the database for the first time may take a while since it
inspects every font file on your computer.
%
This is particularly noticeable if it occurs during a typesetting run.
In any case, subsequent updates to the database will be quite fast.

\beginsubsection[luaotfload-tool]
                {\fileent{luaotfload-tool}}

It can still be desirable at times to do some of these steps
manually, and without having to compile a document.
%
To this end, \identifier{luaotfload} comes with the utility
\fileent{luaotfload-tool} that offers an interface to the database
functionality.
%
Being a \LUA script, there are two ways to run it:
either make it executable (\inlinecode {chmod +x} on unixoid systems) or
pass it as an argument to \fileent{texlua}.\footnote{%
  Tests by the maintainer show only marginal performance gain by
  running with Luigi Scarso’s
  \hyperlink [\identifier{Luajit\kern-.25ex\TEX}]{https://foundry.supelec.fr/projects/luajittex/},
  which is probably due to the fact that most of the time is spent
  on file system operations.

  \emphasis{Note}:
  On \abbrev{MS} \identifier{Windows} systems, the script can be run
  either by calling the wrapper application
  \fileent{luaotfload-tool.exe} or as
  \inlinecode {texlua.exe luaotfload-tool.lua}.
}
%
Invoked with the argument \inlinecode {--update} it will perform a database
update, scanning for fonts not indexed.

\beginlisting
  luaotfload-tool --update
\endlisting

Adding the \inlinecode {--force} switch will initiate a complete
rebuild of the database.

\beginlisting
  luaotfload-tool --update --force
\endlisting

\endsubsection

\beginsubsection{Search Paths}

\identifier{luaotfload} scans those directories where fonts are
expected to be located on a given system.
%
On a Linux machine it follows the paths listed in the
\identifier{Fontconfig} configuration files;
consult \inlinecode {man 5 fonts.conf} for further information.
%
On \identifier{Windows} systems, the standard location is
\inlinecode {Windows\\Fonts},
%
while \identifier{Mac OS~X} requires a multitude of paths to
be examined.
%
The complete list is is given in table \ref{table-searchpaths}.
Other paths can be specified by setting the environment variable
\inlinecode {OSFONTDIR}.
%
If it is non-empty, then search will be extended to the included
directories.

\tablefloat {table-searchpaths}
  {List of paths searched for each supported operating system.}
  {%
    \unless \iffalse
      \begincentered
        \begintabulate [lp{.5\textwidth}]
          \beginrow
            Windows   \newcell \inlinecode !\% WINDIR\%\\ Fonts!
          \endrow
          \beginrow
            Linux     \newcell \fileent{/usr/local/etc/fonts/fonts.conf} and\hfill\break
                               \fileent{/etc/fonts/fonts.conf}
          \endrow
          \beginrow
            Mac       \newcell \fileent{\textasciitilde/Library/Fonts},\break
                               \fileent{/Library/Fonts},\break
                               \fileent{/System/Library/Fonts}, and\hfill\break
                               \fileent{/Network/Library/Fonts}
          \endrow
        \endtabulate
      \endcentered
    \else
      \setuplocalinterlinespace [14pt]
      \starttabulate [|l|p(.5\textwidth)|]
        \NC Windows   \NC \inlinecode {\% WINDIR\%\\ Fonts} \NC \NR
        \NC Linux     \NC \fileent{/usr/local/etc/fonts/fonts.conf} and\crlf
                          \fileent{/etc/fonts/fonts.conf} \NC \NR
        \NC
          Mac         \NC \fileent{\textasciitilde/Library/Fonts},\crlf
                          \fileent{/Library/Fonts},\break
                          \fileent{/System/Library/Fonts}, and\crlf
                          \fileent{/Network/Library/Fonts} \NC \NR
      \stoptabulate
    \fi%
  }

\endsubsection

\beginsubsection{Querying from Outside}

\fileent{luaotfload-tool} also provides rudimentary means of
accessing the information collected in the font database.
%
If the option \inlinecode {--find=}\emphasis{name} is given, the script will
try and search the fonts indexed by \identifier{luaotfload} for a
matching name.
%
For instance, the invocation

\beginlisting
  luaotfload-tool  --find="Iwona Regular"
\endlisting

\noindent
will verify if “Iwona Regular” is found in the database and can be
readily requested in a document.

If you are unsure about the actual font name, then add the
\inlinecode {-F} (or \inlinecode {--fuzzy}) switch to the command line to enable
approximate matching.
%
Suppose you cannot precisely remember if the variant of
\identifier{Iwona} you are looking for was “Bright” or “Light”.
The query

\beginlisting
  luaotfload-tool  -F --find="Iwona Bright"
\endlisting

\noindent
will tell you that indeed the latter name is correct.

Basic information about fonts in the database can be displayed
using the \inlinecode {-i} option (\inlinecode {--info}).
%
\beginlisting
  luaotfload-tool  -i --find="Iwona Light Italic"
\endlisting
%
\noindent
The meaning of the printed values is described in section 4.4 of the
\LUATEX reference manual.\footnote{%
  In \TEX Live: \fileent{texmf-dist/doc/luatex/base/luatexref-t.pdf}.
}

For a much more detailed report about a given font try the
\inlinecode {-I} option instead (\inlinecode {--inspect}).
\beginlisting
  luaotfload-tool  -I --find="Iwona Light Italic"
\endlisting

\inlinecode {luaotfload-tool --help} will list the available command line
switches, including some not discussed in detail here.
%
For a full documentation of \identifier{luaotfload-tool} and its
capabilities refer to the manpage
(\inlinecode {man 1 luaotfload-tool}).\footnote{%
  Or see \inlinecode {luaotfload-tool.rst} in the source directory.
}

\endsubsection

\beginsubsection {Blacklisting Fonts}
\label{font-blacklist}

Some fonts are problematic in general, or just in \LUATEX.
%
If you find that compiling your document takes far too long or eats
away all your system’s memory, you can track down the culprit by
running \inlinecode {luaotfload-tool -v} to increase verbosity.
%
Take a note of the \emphasis{filename} of the font that database
creation fails with and append it to the file
\fileent{luaotfload-blacklist.cnf}.

A blacklist file is a list of font filenames, one per line.
Specifying the full path to where the file is located is optional, the
plain filename should suffice.
%
File extensions (\fileent{.otf}, \fileent{.ttf}, etc.) may be omitted.
%
Anything after a percent (\inlinecode {\%}) character until the end of the line
is ignored, so use this to add comments.
%
Place this file to some location where the \identifier{kpse}
library can find it, e.~g.
\fileent{texmf-local/tex/luatex/luaotfload} if you are running
\identifier{\TEX Live},\footnote{%
  You may have to run \inlinecode {mktexlsr} if you created a new file in
  your \fileent{texmf} tree.
}
or just leave it in the working directory of your document.
%
\identifier{luaotfload} reads all files named
\fileent{luaotfload-blacklist.cnf} it finds, so the fonts in
\fileent{./luaotfload-blacklist.cnf} extend the global blacklist.

Furthermore, a filename prepended with a dash character (\inlinecode{-}) is
removed from the blacklist, causing it to be temporarily whitelisted
without modifying the global file.
%
An example with explicit paths:

\beginlisting
% example otf-blacklist.cnf
/Library/Fonts/GillSans.ttc  % Luaotfload ignores this font.
-/Library/Fonts/Optima.ttc   % This one is usable again, even if
                             % blacklisted somewhere else.
\endlisting

\endsubsection
\endsection

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\beginsection {The Fontloader}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\beginsubsection {Overview}

To a large extent, \identifier{luaotfload} relies on code originally
written by Hans Hagen for the
\hyperlink[\identifier{\CONTEXT}]{http://wiki.contextgarden.net}
format.
%
It integrates the font loader, written entirely in \LUA, as distributed
in the \identifier{\LUATEX-Fonts} package.
%
The original \LUA source files have been combined using the \CONTEXT
packaging library into a single, self-contained blob. In
this form the font loader depends only on the \identifier{lualibs}
package and requires only minor adaptions to integrate into
\identifier{luaotfload}.

The guiding principle is to let \CONTEXT/\LUATEX-Fonts take care of the
implementation, and update the imported code as frequently as
necessary.
%
As maintainers, we aim at importing files from upstream essentially
\emphasis{unmodified}, except for renaming them to prevent name
clashes.
%
This job has been greatly alleviated since the advent of
\LUATEX-Fonts, prior to which the individual dependencies had to be
manually spotted and extracted from the \CONTEXT source code in a
complicated and error-prone fashion.

\endsubsection

\beginsubsection {Contents and Dependencies}

Below is a commented list of the files distributed with
\identifier{luaotfload} in one way or the other.
%
See see the figure on page \pageref{file-graph} for a
graphical representation of the dependencies.
%
\label{package}%
Through the script \fileent{mkimport} a \CONTEXT library
is invoked to create the \identifier{luaotfload} fontloader as a merged
(amalgamated) source file.\footnote{%
  In \CONTEXT, this facility can be accessed by means of a
  \hyperlink[script]{https://bitbucket.org/phg/context-mirror/src/beta/scripts/context/lua/mtx-package.lua?at=beta}
  which is integrated into \fileent{mtxrun} as a subcommand.
  Run \inlinecode {mtxrun --script package --help} to display further
  information.
  For the actual merging code see the file
  \fileent{util-mrg.lua} that is part of \CONTEXT.
}
%
This file constitutes the “default fontloader” and is part of the
\identifier{luaotfload} package as \fileent{fontloader-YY-MM-DD.lua},
where the uppercase letters are placeholders for the build date.
%
A companion to it, \fileent{luatex-basics-gen.lua} (renamed to \fileent{fontloader-basics-gen.lua} in \identifier{luaotfload})
must be loaded beforehand to set up parts of the environment required by the \CONTEXT
libraries.
%
During a \TEX\ run, the fontloader initialization and injection happens
in the module \fileent{luaotfload-init.lua}.
%
Additionally, the “reference fontloader” as imported from \LUATEX-Fonts
is provided as the file \fileent{fontloader-reference.lua}.
%
This file is self-contained in that it packages all the auxiliary \LUA
libraries too, as Luaotfload did up to the 2.5 series; since that job
has been offloaded to the \identifier{Lualibs} package, loading this
fontloader introduces a certain code duplication.

A number of \emphasis{\LUA utility libraries} are not part of the
\identifier{luaotfload} fontloader, contrary to its equivalent in
\LUATEX-Fonts. These are already provided by the \identifier{lualibs}
and have thus been omitted from the merge.\footnote{%
  Faithful listeners will remember the pre-2.6 era when the fontloader
  used to be integrated as-is which caused all kinds of code
  duplication with the pervasive \identifier{lualibs} package.
  This conceptual glitch has since been amended by tightening the
  coupling with the excellent \CONTEXT\ toolchain.
}

\begindoublecolumns
  \begindefinitions
 \directlua{ printctxlibslist ()}
  \enddefinitions
\enddoublecolumns

The reference fontloader is home to several \LUA files that can be
grouped twofold as below:

\begindefinitions
  \beginnormalitem
    The \emphasis{font loader} itself.
    These files have been written for \LUATEX-Fonts and they are
    distributed along with \identifier{luaotfload} so as to resemble
    the state of the code when it was imported. Their purpose is either
    to give a slightly aged version of a file if upstream considers
    latest developments for not yet ready for use outside Context; or,
    to install placeholders or minimalist versions of APIs relied upon
    but usually provided by parts of Context not included in the
    fontloader.
    \begindoublecolumns
      \begindefinitions
        \directlua{printctxallgenericlist ()}
      \enddefinitions
    \enddoublecolumns
  \endnormalitem

  \beginnormalitem
    Code related to \emphasis{font handling and node processing}, taken
    directly from \CONTEXT.
    \begindoublecolumns
      \begindefinitions
      \directlua{printctxfontlist ()}
      \enddefinitions
    \enddoublecolumns
  \endnormalitem
\enddefinitions

As an alternative to the merged file, \identifier {Luaotfload} may load
individual unpackaged \LUA libraries that come with the source, or even
use the files from Context directly.
%
Thus if you prefer running bleeding edge code from the \CONTEXT beta,
choose the \inlinecode {context} fontloader via the configuration file
(see sections \ref{sec:conf} and \ref{sec:pkg} below).

Also, the merged file at some point loads the Adobe Glyph List from a
\LUA table that is contained in \fileent{luaotfload-glyphlist.lua},
which is automatically generated by the script
\fileent{mkglyphlist}.\footnote{%
  See \fileent{luaotfload-font-enc.lua}.
  The hard-coded file name is why we have to replace the procedure
  that loads the file in \fileent{luaotfload-init.lua}.
}
%
There is a make target \identifier{glyphs} that will create a fresh
glyph list so we don’t need to import it from \CONTEXT any longer.

In addition to these, \identifier{luaotfload} requires a number of
files not contained in the merge. Some of these have no equivalent in
\LUATEX-Fonts or \CONTEXT, some were taken unmodified from the latter.


\beginfilelist
    \beginaltitem {luaotfload-features.lua}
      font feature handling; incorporates some of the code from
      \fileent{font-otc} from \CONTEXT;
    \endaltitem
    \beginaltitem {luaotfload-configuration.lua}
      handling of \fileent{luaotfload.conf(5)}.
    \endaltitem
    \beginaltitem {luaotfload-log.lua}
      overrides the \CONTEXT logging functionality.
    \endaltitem
    \beginaltitem {luaotfload-loaders.lua}
      registers readers in the fontloader for various kinds of
      font formats
    \endaltitem
    \beginaltitem {luaotfload-parsers.lua}
      various \abbrev{lpeg}-based parsers.
    \endaltitem
    \beginaltitem {luaotfload-database.lua}
      font names database.
    \endaltitem
    \beginaltitem {luaotfload-resolvers.lua}
      file name resolvers.
    \endaltitem
    \beginaltitem {luaotfload-colors.lua}
      color handling.
    \endaltitem
    \beginaltitem {luaotfload-auxiliary.lua}
      access to internal functionality for package authors (proposals
      for additions welcome).
    \endaltitem
    \beginaltitem {luaotfload-letterspace.lua}
      font-based letterspacing.
    \endaltitem
        \beginaltitem {luaotfload-filelist.lua}
      data about the files in the package.
    \endaltitem
\endfilelist

%\figurefloat
%  {file-graph}
%  {Schematic of the files in \identifier{Luaotfload}}
%  {filegraph.pdf}

\endsubsection

\beginsubsection {Packaging}

\label{sec:pkg}%
The fontloader code is integrated as an isolated component that can be
switched out on demand.
%
To specify the fontloader you wish to use, the configuration file
(described in section \ref{sec:conf}) provides the option
\inlinecode{fontloader}.
%
Its value can be one of the identifiers \inlinecode{default} or
\inlinecode{reference} (see above, section \ref{package}) or the name
of a file somewhere in the search path of \LUATEX.
%
This will make \identifier {Luaotfload} locate the \CONTEXT source by
means of \identifier{kpathsea} lookups and use those instead of the
merged package.
%
The parameter may be extended with a path to the \CONTEXT
\fileent{texmf}, separated with a colon:

\beginlisting
[run]
  fontloader = context:~/context/tex/texmf-context
\endlisting

\noindent This setting allows accessing an installation -- e. g. the
standalone distribution or a source repository -- outside the current
\TEX distribution.

Like the \identifier{Lualibs} package, the fontloader is deployed as a
\emphasis{merged package} containing a series of \LUA files joined
together in their expected order and stripped of non-significant parts.
%
The \fileent{mkimport} utility assists in pulling the files from a
\CONTEXT tree and packaging them for use with \identifier{Luaotfload}.%
%
The state of the files currently in \identifier{Luaotfload}’s
repository can be queried:
\beginlisting
./scripts/mkimport news
\endlisting
%
The subcommand for importing takes the prefix of the desired \CONTEXT
\identifier{texmf} as an optional argument:
\beginlisting
./scripts/mkimport import ~/context/tex/texmf-context
\endlisting
%
Whereas the command for packaging requires a path to the
\emphasis{package description file} and the output name to be passed.
\beginlisting
./scripts/mkimport package fontloader-custom.lua
\endlisting

From the toplevel makefile, the targets \inlinecode{import} and
\inlinecode{package} provide easy access to the commands as invoked during
the \identifier{Luaotfload} build process.\footnote{%
  \emphasis{Hint for those interested in the packaging process}: issue
  \inlinecode{make show} for a list of available build routines.
}
These will call \inlinecode{mkimport} script with the correct
parameters to generate a datestamped package.
%
Whether files have been updated in the upstream distribution can be
queried by \inlinecode{./scripts/mkimport news}.
%
This will compare the imported files with their counterparts in the
\CONTEXT distribution and report changes.

\endsubsection

\endsection

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\beginsection {Configuration Files}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\beginnarrower
  \emphasis{Caution}: For the authoritative documentation, consult the
  manpage for \fileent{luaotfload.conf(5)}.
\endnarrower

\label{sec:conf}
The runtime behavior of \identifier{Luaotfload} can be customized by
means of a configuration file.
% location
At startup, it attempts to locate a file called \fileent
{luaotfload.conf} or \fileent {luaotfloadrc} at a number of candidate
locations:

\begincentered
  \begindefinitions
    \beginnormalitem \fileent{./luaotfload.conf}                            \endnormalitem
    \beginnormalitem \fileent{./luaotfloadrc}                               \endnormalitem
    \beginnormalitem \fileent{\$XDG_CONFIG_HOME/luaotfload/luaotfload.conf} \endnormalitem
    \beginnormalitem \fileent{\$XDG_CONFIG_HOME/luaotfload/luaotfload.rc}   \endnormalitem
    \beginnormalitem \fileent{~/.luaotfloadrc}                              \endnormalitem
  \enddefinitions
\endcentered

\beginnarrower
  \emphasis{Caution}: The configuration potentially modifies the final
  document. A project-local file belongs under version control along
  with the rest of the document. This is to ensure that everybody who
  builds the project also receives the same customizations as the
  author.
\endnarrower

% syntax
The syntax is fairly close to the format used by
\fileent{git-config(1)} which in turn was derived from the popular
\identifier{.INI} format: Lines of key-value pairs are grouped under
different configuration “sections”.\footnote{%
  The configuration parser in \fileent {luoatfload-parsers.lua} might
  be employed by other packages for similar purposes.
}
% example settings
An example for customization via \fileent {luaotfload.conf} might look
as below:

\beginlisting
; Example luaotfload.conf containing a rudimentary configuration
[db]
  update-live = false
[run]
  color-callback = pre_linebreak_filter
  definer = info_patch
  log-level = 5
[default-features]
  global = mode=base
\endlisting

This specifies that for the given project, \identifier{Luaotfload}
shall not attempt to automatically scan for fonts if it can’t resolve a
request. The font-based colorization will happen during \LUATEX’s
pre-linebreak filter. The fontloader will output verbose information
about the fonts at definition time along with globally increased
verbosity. Lastly, the fontloader defaults to the less expensive
\luaident{base} mode like it does in \CONTEXT.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\beginsection {Auxiliary Functions}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

With release version 2.2, \identifier{Luaotfload} received
additional functions for package authors to call from outside
(see the file \fileent{luaotfload-auxiliary.lua} for details).
%
The purpose of this addition twofold.
%
Firstly, \identifier{luaotfload} failed to provide a stable interface
to internals in the past which resulted in an unmanageable situation
of different packages abusing the raw access to font objects by means
of the \luaident{patch_font} callback.
%
When the structure of the font object changed due to an update, all
of these imploded and several packages had to be fixed while
simultaneously providing fallbacks for earlier versions.
%
Now the patching is done on the \identifier{luaotfload} side and can
be adapted with future modifications to font objects without touching
the packages that depend on it.
%
Second, some the capabilities of the font loader and the names
database are not immediately relevant in \identifier{luaotfload}
itself but might nevertheless be of great value to package authors or
end users.

Note that the current interface is not yet set in stone and the
development team is open to suggestions for improvements or
additions.

\beginsubsection {Callback Functions}

The \luaident{patch_font} callback is inserted in the wrapper
\identifier{luaotfload} provides for the font definition callback.
%
At this place it allows manipulating the font object immediately after
the font loader is done creating it.
%
For a short demonstration of its usefulness, here is a snippet that
writes an entire font object to the file \fileent{fontdump.lua}:

\beginlisting
  \input luaotfload.sty
  \directlua{
    local dumpfile    = "fontdump.lua"
    local dump_font   = function (tfmdata)
      local data = table.serialize(tfmdata)
      io.savedata(dumpfile, data)
    end

    luatexbase.add_to_callback(
      "luaotfload.patch_font",
      dump_font,
      "my_private_callbacks.dump_font"
    )
  }
  \font \dumpme = name:Iwona
  \bye
\endlisting

\emphasis{Beware}: this creates a Lua file of around 150,000 lines of
code, taking up 3~\abbrev{mb} of disk space.
%
By inspecting the output you can get a first impression of how a font
is structured in \LUATEX’s memory, what elements it is composed of,
and in what ways it can be rearranged.

\beginsubsubsection {Compatibility with Earlier Versions}

As has been touched on in the preface to this section, the structure
of the object as returned by the fontloader underwent rather drastic
changes during different stages of its development, and not all
packages that made use of font patching have kept up with every one
of it.
%
To ensure compatibility with these as well as older versions of
some packages, \identifier{luaotfload} sets up copies of or references
to data in the font table where it used to be located.
%
For instance, important parameters like the requested point size, the
units factor, and the font name have again been made accessible from
the toplevel of the table even though they were migrated to different
subtables in the meantime.

\endsubsubsection

\beginsubsubsection{Patches}

These are mostly concerned with establishing compatibility with \XETEX.

\beginfunctionlist

  \beginaltitem  {set_sscale_dimens}
    Calculate \texmacro{fontdimen}s 10 and 11 to emulate \XETEX.
  \endaltitem

  \beginaltitem  {set_capheight}
    Calculates \texmacro{fontdimen} 8 like \XETEX.
  \endaltitem

  \beginaltitem  {patch_cambria_domh}
    Correct some values of the font \emphasis{Cambria Math}.
  \endaltitem

\endfunctionlist

\endsubsection

\beginsubsection {Package Author’s Interface}

As \LUATEX release 1.0 is nearing, the demand for a reliable interface
for package authors increases.

\endsubsubsection

\beginsubsubsection{Font Properties}

Below functions mostly concern querying the different components of a
font like for instance the glyphs it contains, or what font features
are defined for which scripts.

\beginfunctionlist

  \beginaltitem  {aux.font_has_glyph (id : int, index : int)}
            Predicate that returns true if the font \luaident{id}
            has glyph \luaident{index}.
  \endaltitem

  \beginaltitem  {aux.slot_of_name(name : string)}
            Translates an Adobe Glyph name to the corresponding glyph
            slot.
  \endaltitem

  \beginaltitem  {aux.name_of_slot(slot : int)}
            The inverse of \luaident{slot_of_name}; note that this
            might be incomplete as multiple glyph names may map to the
            same codepoint, only one of which is returned by
            \luaident{name_of_slot}.
  \endaltitem

  \beginaltitem  {aux.provides_script(id : int, script : string)}
            Test if a font supports \luaident{script}.
  \endaltitem

  \beginaltitem  {aux.provides_language(id : int, script : string, language : string)}
            Test if a font defines \luaident{language} for a given
            \luaident{script}.
  \endaltitem

  \beginaltitem  {aux.provides_feature(id : int, script : string,
             language : string, feature : string)}
            Test if a font defines \luaident{feature} for
            \luaident{language} for a given \luaident{script}.
  \endaltitem

  \beginaltitem  {aux.get_math_dimension(id : int, dimension : string)}
            Get the dimension \luaident{dimension} of font \luaident{id}.
  \endaltitem

  \beginaltitem  {aux.sprint_math_dimension(id : int, dimension : string)}
            Same as \luaident{get_math_dimension()}, but output the value
            in scaled points at the \TEX end.
  \endaltitem

\endfunctionlist

\endsubsubsection

\beginsubsubsection{Database}

%% not implemented, may come back later
\beginfunctionlist
%   \beginaltitem  {aux.scan_external_dir(dir : string)}
%             Include fonts in directory \luaident{dir} in font lookups without
%             adding them to the database.
%
  \beginaltitem  {aux.read_font_index (void)}
            Read the index file from the appropriate location (usually
            the bytecode file \fileent{luaotfload-names.luc} somewhere
            in the \fileent{texmf-var} tree) and return the result as a
            table. The file is processed with each call so it is up to
            the user to store the result for later access.
  \endaltitem

  \beginaltitem  {aux.font_index (void)}
            Return a reference of the font names table used internally
            by \identifier{luaotfload}. The index will be read if it
            has not been loaded up to this point. Also a font scan that
            overwrites the current index file might be triggered. Since
            the return value points to the actual index, any
            modifications to the table might influence runtime behavior
            of \identifier{luaotfload}.
  \endaltitem

\endfunctionlist

\endsubsubsection

\endsubsection
\endsection

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\beginsection {Troubleshooting}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\beginsubsection {Database Generation}

If you encounter problems with some fonts, please first update to the
latest version of this package before reporting a bug, as
\identifier{luaotfload} is under active development and still a moving
target.
%
The development takes place on \identifier{github} at
\hyperlink {https://github.com/lualatex/luaotfload} where there is an issue
tracker for submitting bug reports, feature requests and the likes.

Bug reports are more likely to be addressed if they contain the output
of

\beginlisting
    luaotfload-tool --diagnose=environment,files,permissions
\endlisting

\noindent Consult the man page for a description of these options.

Errors during database generation can be traced by increasing the
verbosity level and redirecting log output to \fileent{stdout}:

\beginlisting
    luaotfload-tool -fuvvv --log=stdout
\endlisting

\noindent or to a file in \fileent{/tmp}:

\beginlisting
    luaotfload-tool -fuvvv --log=file
\endlisting

\noindent In the latter case, invoke the \inlinecode {tail(1)} utility on the
file for live monitoring of the progress.

If database generation fails, the font last printed to the terminal or
log file is likely to be the culprit.
%
Please specify it when reporting a bug, and blacklist it for the time
being (see above, page \pageref{font-blacklist}).

\endsubsection

\beginsubsection {Font Features}

A common problem is the lack of features for some
\OpenType fonts even when specified.
%
This can be related to the fact that some fonts do not provide features
for the \inlinecode {dflt} script (see above on page \pageref{script-tag}),
which is the default one in this package.
%
If this happens, assigning a noth script when the font is defined should
fix it.
%
For example with \inlinecode {latn}:

\beginlisting
    \font \test = file:MyFont.otf:script=latn;+liga;
\endlisting

You can get a list of features that a font defines for scripts and
languages by querying it in \fileent{luaotfload-tool}:

\beginlisting
    luaotfload-tool --find="Iwona" --inspect
\endlisting

\endsubsection

\beginsubsection {\LUATEX Programming}

Another strategy that helps avoiding problems is to not access raw
\LUATEX internals directly.
%
Some of them, even though they are dangerous to access, have not been
overridden or disabled.
%
Thus, whenever possible prefer the functions in the \luaident{aux}
namespace over direct manipulation of font objects. For example, raw
access to the \luaident{font.fonts} table like:

\beginlisting
    local somefont = font.fonts[2]
\endlisting

\noindent can render already defined fonts unusable.
%
Instead, the function \luaident{font.getfont()} should be used
because it has been replaced by a safe variant.

However, \luaident{font.getfont()} only covers fonts handled by the
font loader, e.~g. \identifier{OpenType} and \identifier{TrueType}
fonts, but not \abbrev{tfm} or \abbrev{ofm}.
%
Should you absolutely require access to all fonts known to \LUATEX,
including the virtual and autogenerated ones, then you need to query
both \luaident{font.getfont()} and \luaident{font.fonts}.
%
In this case, best define you own accessor:

\beginlisting
    local unsafe_getfont = function (id)
        local tfmdata = font.getfont (id)
        if not tfmdata then
            tfmdata = font.fonts[id]
        end
        return tfmdata
    end

    --- use like getfont()
    local somefont = unsafe_getfont (2)
\endlisting

\endsubsection
\endsection

\beginsection {License}

\identifier {luaotfload} is licensed under the terms of the
\hyperlink [GNU General Public License version 2.0]%
           {https://www.gnu.org/licenses/old-licenses/gpl-2.0.html}.
Following the underlying fontloader code \identifier {luaotfload}
recognizes only that exact version as its license.
The „any later version” clause of the original license text as
copyrighted by the \hyperlink [Free Software Foundation]{http://www.fsf.org/}
\emphasis {does not apply} to either \identifier {luaotfload} or the
code imported from \CONTEXT.

The complete text of the license is given as a separate file \fileent
{COPYING} in the toplevel directory of the
\hyperlink [\fileent {Luaotfload} Git repository]{https://github.com/lualatex/luaotfload/blob/master/COPYING}.\\
Distributions probably package it as \fileent
{doc/luatex/luaotfload/COPYING} in the relevant \fileent {texmf} tree.

\endsection

\endinput

% vim:ft=tex:tw=79:et:sw=2