summaryrefslogtreecommitdiff
path: root/macros/luatex/generic/penlight/pl/xml.lua
blob: 4650a32099f9931d649602bc2c773889af459641 (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
--- XML LOM Utilities.
--
-- This implements some useful things on [LOM](http://matthewwild.co.uk/projects/luaexpat/lom.html) documents, such as returned by `lxp.lom.parse`.
-- In particular, it can convert LOM back into XML text, with optional pretty-printing control.
-- It is s based on stanza.lua from [Prosody](http://hg.prosody.im/trunk/file/4621c92d2368/util/stanza.lua)
--
--     > d = xml.parse "<nodes><node id='1'>alice</node></nodes>"
--     > = d
--     <nodes><node id='1'>alice</node></nodes>
--     > = xml.tostring(d,'','  ')
--     <nodes>
--        <node id='1'>alice</node>
--     </nodes>
--
-- Can be used as a lightweight one-stop-shop for simple XML processing; a simple XML parser is included
-- but the default is to use `lxp.lom` if it can be found.
-- <pre>
-- Prosody IM
-- Copyright (C) 2008-2010 Matthew Wild
-- Copyright (C) 2008-2010 Waqas Hussain--
-- classic Lua XML parser by Roberto Ierusalimschy.
-- modified to output LOM format.
-- http://lua-users.org/wiki/LuaXml
-- </pre>
-- See @{06-data.md.XML|the Guide}
--
-- Dependencies: `pl.utils`
--
-- Soft Dependencies: `lxp.lom` (fallback is to use basic Lua parser)
-- @module pl.xml

local utils = require 'pl.utils'
local split         =   utils.split;
local t_insert      =  table.insert;
local t_concat      =  table.concat;
local t_remove      =  table.remove;
local s_match       =  string.match;
local tostring      =      tostring;
local setmetatable  =  setmetatable;
local getmetatable  =  getmetatable;
local pairs         =         pairs;
local ipairs        =        ipairs;
local type          =          type;
local next          =          next;
local print         =         print;
local unpack        =  utils.unpack;
local s_gsub        =   string.gsub;
local s_find        =   string.find;
local pcall,require,io     =   pcall,require,io

local _M = {}
local Doc = { __type = "doc" };
Doc.__index = Doc;

--- create a new document node.
-- @param tag the tag name
-- @param attr optional attributes (table of name-value pairs)
function _M.new(tag, attr)
    local doc = { tag = tag, attr = attr or {}, last_add = {}};
    return setmetatable(doc, Doc);
end

--- parse an XML document.  By default, this uses lxp.lom.parse, but
-- falls back to basic_parse, or if use_basic is true
-- @param text_or_file  file or string representation
-- @param is_file whether text_or_file is a file name or not
-- @param use_basic do a basic parse
-- @return a parsed LOM document with the document metatatables set
-- @return nil, error the error can either be a file error or a parse error
function _M.parse(text_or_file, is_file, use_basic)
    local parser,status,lom
    if use_basic then parser = _M.basic_parse
    else
        status,lom = pcall(require,'lxp.lom')
        if not status then parser = _M.basic_parse else parser = lom.parse end
    end
    if is_file then
        local f,err = io.open(text_or_file)
        if not f then return nil,err end
        text_or_file = f:read '*a'
        f:close()
    end
    local doc,err = parser(text_or_file)
    if not doc then return nil,err end
    if lom then
        _M.walk(doc,false,function(_,d)
            setmetatable(d,Doc)
        end)
    end
    return doc
end

---- convenient function to add a document node, This updates the last inserted position.
-- @param tag a tag name
-- @param attrs optional set of attributes (name-string pairs)
function Doc:addtag(tag, attrs)
    local s = _M.new(tag, attrs);
    (self.last_add[#self.last_add] or self):add_direct_child(s);
    t_insert(self.last_add, s);
    return self;
end

--- convenient function to add a text node.  This updates the last inserted position.
-- @param text a string
function Doc:text(text)
    (self.last_add[#self.last_add] or self):add_direct_child(text);
    return self;
end

---- go up one level in a document
function Doc:up()
    t_remove(self.last_add);
    return self;
end

function Doc:reset()
    local last_add = self.last_add;
    for i = 1,#last_add do
        last_add[i] = nil;
    end
    return self;
end

--- append a child to a document directly.
-- @param child a child node (either text or a document)
function Doc:add_direct_child(child)
    t_insert(self, child);
end

--- append a child to a document at the last element added
-- @param child a child node (either text or a document)
function Doc:add_child(child)
    (self.last_add[#self.last_add] or self):add_direct_child(child);
    return self;
end

--accessing attributes: useful not to have to expose implementation (attr)
--but also can allow attr to be nil in any future optimizations

--- set attributes of a document node.
-- @param t a table containing attribute/value pairs
function Doc:set_attribs (t)
    for k,v in pairs(t) do
        self.attr[k] = v
    end
end

--- set a single attribute of a document node.
-- @param a attribute
-- @param v its value
function Doc:set_attrib(a,v)
    self.attr[a] = v
end

--- access the attributes of a document node.
function Doc:get_attribs()
    return self.attr
end

local function is_text(s) return type(s) == 'string' end

--- function to create an element with a given tag name and a set of children.
-- @param tag a tag name
-- @param items either text or a table where the hash part is the attributes and the list part is the children.
function _M.elem(tag,items)
    local s = _M.new(tag)
    if is_text(items) then items = {items} end
    if _M.is_tag(items) then
       t_insert(s,items)
    elseif type(items) == 'table' then
       for k,v in pairs(items) do
           if is_text(k) then
               s.attr[k] = v
               t_insert(s.attr,k)
           else
               s[k] = v
           end
       end
    end
    return s
end

--- given a list of names, return a number of element constructors.
-- @param list  a list of names, or a comma-separated string.
-- @usage local parent,children = doc.tags 'parent,children' <br>
--  doc = parent {child 'one', child 'two'}
function _M.tags(list)
    local ctors = {}
    if is_text(list) then list = split(list,'%s*,%s*') end
    for _,tag in ipairs(list) do
        local ctor = function(items) return _M.elem(tag,items) end
        t_insert(ctors,ctor)
    end
    return unpack(ctors)
end

local templ_cache = {}

local function template_cache (templ)
    if is_text(templ) then
        if templ_cache[templ] then
            templ = templ_cache[templ]
        else
            local str,err = templ
            templ,err = _M.parse(str,false,true)
            if not templ then return nil,err end
            templ_cache[str] = templ
        end
    elseif not _M.is_tag(templ) then
        return nil, "template is not a document"
    end
    return templ
end

local function is_data(data)
    return #data == 0 or type(data[1]) ~= 'table'
end

local function prepare_data(data)
    -- a hack for ensuring that $1 maps to first element of data, etc.
    -- Either this or could change the gsub call just below.
    for i,v in ipairs(data) do
        data[tostring(i)] = v
    end
end

--- create a substituted copy of a document,
-- @param templ  may be a document or a string representation which will be parsed and cached
-- @param data  a table of name-value pairs or a list of such tables
-- @return an XML document
function Doc.subst(templ, data)
    local err
    if type(data) ~= 'table' or not next(data) then return nil, "data must be a non-empty table" end
    if is_data(data) then
        prepare_data(data)
    end
    templ,err = template_cache(templ)
    if err then return nil, err end
    local function _subst(item)
        return _M.clone(templ,function(s)
            return s:gsub('%$(%w+)',item)
        end)
    end
    if is_data(data) then return _subst(data) end
    local list = {}
    for _,item in ipairs(data) do
        prepare_data(item)
        t_insert(list,_subst(item))
    end
    if data.tag then
        list = _M.elem(data.tag,list)
    end
    return list
end


--- get the first child with a given tag name.
-- @param tag the tag name
function Doc:child_with_name(tag)
    for _, child in ipairs(self) do
        if child.tag == tag then return child; end
    end
end

local _children_with_name
function _children_with_name(self,tag,list,recurse)
    for _, child in ipairs(self) do if type(child) == 'table' then
        if child.tag == tag then t_insert(list,child) end
        if recurse then _children_with_name(child,tag,list,recurse) end
    end end
end

--- get all elements in a document that have a given tag.
-- @param tag a tag name
-- @param dont_recurse optionally only return the immediate children with this tag name
-- @return a list of elements
function Doc:get_elements_with_name(tag,dont_recurse)
    local res = {}
    _children_with_name(self,tag,res,not dont_recurse)
    return res
end

-- iterate over all children of a document node, including text nodes.
function Doc:children()
    local i = 0;
    return function (a)
            i = i + 1
            return a[i];
    end, self, i;
end

-- return the first child element of a node, if it exists.
function Doc:first_childtag()
    if #self == 0 then return end
    for _,t in ipairs(self) do
        if type(t) == 'table' then return t end
    end
end

function Doc:matching_tags(tag, xmlns)
    xmlns = xmlns or self.attr.xmlns;
    local tags = self;
    local start_i, max_i, v = 1, #tags;
    return function ()
            for i=start_i,max_i do
                v = tags[i];
                if (not tag or v.tag == tag)
                and (not xmlns or xmlns == v.attr.xmlns) then
                    start_i = i+1;
                    return v;
                end
            end
        end, tags, start_i;
end

--- iterate over all child elements of a document node.
function Doc:childtags()
    local i = 0;
    return function (a)
        local v
            repeat
                i = i + 1
                v = self[i]
                if v and type(v) == 'table' then return v; end
            until not v
        end, self[1], i;
end

--- visit child element  of a node and call a function, possibility modifying the document.
-- @param callback  a function passed the node (text or element). If it returns nil, that node will be removed.
-- If it returns a value, that will replace the current node.
function Doc:maptags(callback)
    local is_tag = _M.is_tag
    local i = 1;
    while i <= #self do
        if is_tag(self[i]) then
            local ret = callback(self[i]);
            if ret == nil then
                t_remove(self, i);
            else
                self[i] = ret;
                i = i + 1;
            end
        end
    end
    return self;
end

local xml_escape
do
    local escape_table = { ["'"] = "&apos;", ["\""] = "&quot;", ["<"] = "&lt;", [">"] = "&gt;", ["&"] = "&amp;" };
    function xml_escape(str) return (s_gsub(str, "['&<>\"]", escape_table)); end
    _M.xml_escape = xml_escape;
end

-- pretty printing
-- if indent, then put each new tag on its own line
-- if attr_indent, put each new attribute on its own line
local function _dostring(t, buf, self, xml_escape, parentns, idn, indent, attr_indent)
    local nsid = 0;
    local tag = t.tag
    local lf,alf = ""," "
    if indent then lf = '\n'..idn end
    if attr_indent then alf = '\n'..idn..attr_indent end
    t_insert(buf, lf.."<"..tag);
    local function write_attr(k,v)
        if s_find(k, "\1", 1, true) then
            local ns, attrk = s_match(k, "^([^\1]*)\1?(.*)$");
            nsid = nsid + 1;
            t_insert(buf, " xmlns:ns"..nsid.."='"..xml_escape(ns).."' ".."ns"..nsid..":"..attrk.."='"..xml_escape(v).."'");
        elseif not(k == "xmlns" and v == parentns) then
            t_insert(buf, alf..k.."='"..xml_escape(v).."'");
        end
    end
    -- it's useful for testing to have predictable attribute ordering, if available
    if #t.attr > 0 then
        for _,k in ipairs(t.attr) do
            write_attr(k,t.attr[k])
        end
    else
        for k, v in pairs(t.attr) do
            write_attr(k,v)
        end
    end
    local len,has_children = #t;
    if len == 0 then
    local out = "/>"
    if attr_indent then out = '\n'..idn..out end
        t_insert(buf, out);
    else
        t_insert(buf, ">");
        for n=1,len do
            local child = t[n];
            if child.tag then
                self(child, buf, self, xml_escape, t.attr.xmlns,idn and idn..indent, indent, attr_indent );
                has_children = true
            else -- text element
                t_insert(buf, xml_escape(child));
            end
        end
        t_insert(buf, (has_children and lf or '').."</"..tag..">");
    end
end

---- pretty-print an XML document
--- @param t an XML document
--- @param idn an initial indent (indents are all strings)
--- @param indent an indent for each level
--- @param attr_indent if given, indent each attribute pair and put on a separate line
--- @param xml force prefacing with default or custom <?xml...>
--- @return a string representation
function _M.tostring(t,idn,indent, attr_indent, xml)
    local buf = {};
    if xml then
        if type(xml) == "string" then
            buf[1] = xml
        else
            buf[1] = "<?xml version='1.0'?>"
        end
    end
    _dostring(t, buf, _dostring, xml_escape, nil,idn,indent, attr_indent);
    return t_concat(buf);
end

Doc.__tostring = _M.tostring

--- get the full text value of an element
function Doc:get_text()
    local res = {}
    for i,el in ipairs(self) do
        if is_text(el) then t_insert(res,el) end
    end
    return t_concat(res);
end

--- make a copy of a document
-- @param doc the original document
-- @param strsubst an optional function for handling string copying which could do substitution, etc.
function _M.clone(doc, strsubst)
    local lookup_table = {};
    local function _copy(object,kind,parent)
        if type(object) ~= "table" then
            if strsubst and is_text(object) then return strsubst(object,kind,parent)
            else return object
            end
        elseif lookup_table[object] then
            return lookup_table[object]
        end
        local new_table = {};
        lookup_table[object] = new_table
        local tag = object.tag
        new_table.tag = _copy(tag,'*TAG',parent)
        if object.attr then
            local res = {}
            for attr,value in pairs(object.attr) do
                res[attr] = _copy(value,attr,object)
            end
            new_table.attr = res
        end
        for index = 1,#object do
            local v = _copy(object[index],'*TEXT',object)
            t_insert(new_table,v)
        end
        return setmetatable(new_table, getmetatable(object))
    end

    return _copy(doc)
end

Doc.filter = _M.clone -- also available as method

--- compare two documents.
-- @param t1 any value
-- @param t2 any value
function _M.compare(t1,t2)
    local ty1 = type(t1)
    local ty2 = type(t2)
    if ty1 ~= ty2 then return false, 'type mismatch' end
    if ty1 == 'string' then
        return t1 == t2 and true or 'text '..t1..' ~= text '..t2
    end
    if ty1 ~= 'table' or ty2 ~= 'table' then return false, 'not a document' end
    if t1.tag ~= t2.tag then return false, 'tag  '..t1.tag..' ~= tag '..t2.tag end
    if #t1 ~= #t2 then return false, 'size '..#t1..' ~= size '..#t2..' for tag '..t1.tag end
    -- compare attributes
    for k,v in pairs(t1.attr) do
        if t2.attr[k] ~= v then return false, 'mismatch attrib' end
    end
    for k,v in pairs(t2.attr) do
        if t1.attr[k] ~= v then return false, 'mismatch attrib' end
    end
    -- compare children
    for i = 1,#t1 do
        local yes,err = _M.compare(t1[i],t2[i])
        if not yes then return err end
    end
    return true
end

--- is this value a document element?
-- @param d any value
function _M.is_tag(d)
    return type(d) == 'table' and is_text(d.tag)
end

--- call the desired function recursively over the document.
-- @param doc the document
-- @param depth_first  visit child notes first, then the current node
-- @param operation a function which will receive the current tag name and current node.
function _M.walk (doc, depth_first, operation)
    if not depth_first then operation(doc.tag,doc) end
    for _,d in ipairs(doc) do
        if _M.is_tag(d) then
            _M.walk(d,depth_first,operation)
        end
    end
    if depth_first then operation(doc.tag,doc) end
end

local html_empty_elements = { --lists all HTML empty (void) elements
    br      = true,
    img     = true,
    meta    = true,
    frame   = true,
    area    = true,
    hr      = true,
    base    = true,
    col     = true,
    link    = true,
    input   = true,
    option  = true,
    param   = true,
    isindex = true,
    embed = true,
}

local escapes = { quot = "\"", apos = "'", lt = "<", gt = ">", amp = "&" }
local function unescape(str) return (str:gsub( "&(%a+);", escapes)); end

--- Parse a well-formed HTML file as a string.
-- Tags are case-insenstive, DOCTYPE is ignored, and empty elements can be .. empty.
-- @param s the HTML
function _M.parsehtml (s)
    return _M.basic_parse(s,false,true)
end

--- Parse a simple XML document using a pure Lua parser based on Robero Ierusalimschy's original version.
-- @param s the XML document to be parsed.
-- @param all_text  if true, preserves all whitespace. Otherwise only text containing non-whitespace is included.
-- @param html if true, uses relaxed HTML rules for parsing
function _M.basic_parse(s,all_text,html)
    local t_insert,t_remove = table.insert,table.remove
    local s_find,s_sub = string.find,string.sub
    local stack = {}
    local top = {}

    local function parseargs(s)
      local arg = {}
      s:gsub("([%w:%-_]+)%s*=%s*([\"'])(.-)%2", function (w, _, a)
        if html then w = w:lower() end
        arg[w] = unescape(a)
      end)
      if html then
        s:gsub("([%w:%-_]+)%s*=%s*([^\"']+)%s*", function (w, a)
          w = w:lower()
          arg[w] = unescape(a)
        end)
      end
      return arg
    end

    t_insert(stack, top)
    local ni,c,label,xarg, empty, _, istart
    local i = 1
    local j
    -- we're not interested in <?xml version="1.0"?>
    _,istart = s_find(s,'^%s*<%?[^%?]+%?>%s*')
    if not istart then -- or <!DOCTYPE ...>
        _,istart = s_find(s,'^%s*<!DOCTYPE.->%s*')
    end
    if istart then i = istart+1 end
    while true do
        ni,j,c,label,xarg, empty = s_find(s, "<([%/!]?)([%w:%-_]+)(.-)(%/?)>", i)
        if not ni then break end
        if c == "!" then -- comment
            -- case where there's no space inside comment
            if not (label:match '%-%-$' and xarg == '') then
                if xarg:match '%-%-$' then -- we've grabbed it all
                    j = j - 2
                end
                -- match end of comment
                _,j = s_find(s, "-->", j, true)
            end
        else
            local text = s_sub(s, i, ni-1)
            if html then
                label = label:lower()
                if html_empty_elements[label] then empty = "/" end
            end
            if all_text or not s_find(text, "^%s*$") then
                t_insert(top, unescape(text))
            end
            if empty == "/" then  -- empty element tag
                t_insert(top, setmetatable({tag=label, attr=parseargs(xarg), empty=1},Doc))
            elseif c == "" then   -- start tag
                top = setmetatable({tag=label, attr=parseargs(xarg)},Doc)
                t_insert(stack, top)   -- new level
            else  -- end tag
                local toclose = t_remove(stack)  -- remove top
                top = stack[#stack]
                if #stack < 1 then
                    error("nothing to close with "..label..':'..text)
                end
                if toclose.tag ~= label then
                    error("trying to close "..toclose.tag.." with "..label.." "..text)
                end
                t_insert(top, toclose)
            end
        end
        i = j+1
    end
    local text = s_sub(s, i)
    if all_text or  not s_find(text, "^%s*$") then
        t_insert(stack[#stack], unescape(text))
    end
    if #stack > 1 then
        error("unclosed "..stack[#stack].tag)
    end
    local res = stack[1]
    return is_text(res[1]) and res[2] or res[1]
end

local function empty(attr) return not attr or not next(attr) end
local function is_element(d) return type(d) == 'table' and d.tag ~= nil end

-- returns the key,value pair from a table if it has exactly one entry
local function has_one_element(t)
    local key,value = next(t)
    if next(t,key) ~= nil then return false end
    return key,value
end

local function append_capture(res,tbl)
    if not empty(tbl) then -- no point in capturing empty tables...
        local key
        if tbl._ then  -- if $_ was set then it is meant as the top-level key for the captured table
            key = tbl._
            tbl._ = nil
            if empty(tbl) then return end
        end
        -- a table with only one pair {[0]=value} shall be reduced to that value
        local numkey,val = has_one_element(tbl)
        if numkey == 0 then tbl = val end
        if key then
            res[key] = tbl
        else -- otherwise, we append the captured table
            t_insert(res,tbl)
        end
    end
end

local function make_number(pat)
    if pat:find '^%d+$' then -- $1 etc means use this as an array location
        pat = tonumber(pat)
    end
    return pat
end

local function capture_attrib(res,pat,value)
    pat = make_number(pat:sub(2))
    res[pat] = value
    return true
end

local match
function match(d,pat,res,keep_going)
    local ret = true
    if d == nil then d = '' end --return false end
    -- attribute string matching is straight equality, except if the pattern is a $ capture,
    -- which always succeeds.
    if is_text(d) then
        if not is_text(pat) then return false end
        if _M.debug then print(d,pat) end
        if pat:find '^%$' then
            return capture_attrib(res,pat,d)
        else
            return d == pat
        end
    else
    if _M.debug then print(d.tag,pat.tag) end
        -- this is an element node. For a match to succeed, the attributes must
        -- match as well.
        -- a tagname in the pattern ending with '-' is a wildcard and matches like an attribute
        local tagpat = pat.tag:match '^(.-)%-$'
        if tagpat then
            tagpat = make_number(tagpat)
            res[tagpat] = d.tag
        end
        if d.tag == pat.tag or tagpat then

            if not empty(pat.attr) then
                if empty(d.attr) then ret =  false
                else
                    for prop,pval in pairs(pat.attr) do
                        local dval = d.attr[prop]
                        if not match(dval,pval,res) then ret = false;  break end
                    end
                end
            end
            -- the pattern may have child nodes. We match partially, so that {P1,P2} shall match {X,P1,X,X,P2,..}
            if ret and #pat > 0 then
                local i,j = 1,1
                local function next_elem()
                    j = j + 1  -- next child element of data
                    if is_text(d[j]) then j = j + 1 end
                    return j <= #d
                end
                repeat
                    local p = pat[i]
                    -- repeated {{<...>}} patterns  shall match one or more elements
                    -- so e.g. {P+} will match {X,X,P,P,X,P,X,X,X}
                    if is_element(p) and p.repeated then
                        local found
                        repeat
                            local tbl = {}
                            ret = match(d[j],p,tbl,false)
                            if ret then
                                found = false --true
                                append_capture(res,tbl)
                            end
                        until not next_elem() or (found and not ret)
                        i = i + 1
                    else
                        ret = match(d[j],p,res,false)
                        if ret then i = i + 1 end
                    end
                until not next_elem() or i > #pat -- run out of elements or patterns to match
                -- if every element in our pattern matched ok, then it's been a successful match
                if i > #pat then return true end
            end
            if ret then return true end
        else
            ret = false
        end
        -- keep going anyway - look at the children!
        if keep_going then
            for child in d:childtags() do
                ret = match(child,pat,res,keep_going)
                if ret then break end
            end
        end
    end
    return ret
end

function Doc:match(pat)
    local err
    pat,err = template_cache(pat)
    if not pat then return nil, err end
    _M.walk(pat,false,function(_,d)
        if is_text(d[1]) and is_element(d[2]) and is_text(d[3]) and
           d[1]:find '%s*{{' and d[3]:find '}}%s*' then
           t_remove(d,1)
           t_remove(d,2)
           d[1].repeated = true
        end
    end)

    local res = {}
    local ret = match(self,pat,res,true)
    return res,ret
end


return _M