File: dtd_pl.html

package info (click to toggle)
perlsgml 1996Oct09-6
  • links: PTS
  • area: main
  • in suites: hamm
  • size: 2,452 kB
  • ctags: 792
  • sloc: perl: 4,639; makefile: 167
file content (1502 lines) | stat: -rw-r--r-- 38,609 bytes parent folder | download
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
<html>
<head>
<title>dtd.pl 2.4.0</title>
</head>
<body>

<!-- =================================================================== -->
<hr>
<h1>dtd.pl</h1>

<p><code>dtd.pl</code> is a <a
href="http://www.cis.ufl.edu/perl/">Perl</a> 4 library that parses an
<a href="http://www.sil.org/sgml/sgml.html">SGML</a> document type
defintion (DTD) and creates Perl data structures containing the
content of the DTD.  </p>

<dl>
<dt><strong>Note</strong></dt>

    <dd><p>The library is useable under Perl 5 systems.  However, only
    Perl 4 constructs are used.  </p></dd>

</dl>

<!-- =================================================================== -->
<hr>
<h2><a name="audience">Audience</a></h2>

<p>I assume the reader knows about the scope of packages and how to
access variables/subroutines defined in packages. If not, refer to
<code>perl</code>(1) or any book on Perl.  The reader should also
have a working knowledge of SGML.  </p>

<p>Unless stated, or implied, otherwise, all variables mentioned are
within the scope of package <code>dtd</code>.  </p>

<!-- =================================================================== -->
<hr>
<h2><a name="usage">Usage</a></h2>

<p>Once installed, the following statement can be used to access the
<code>dtd</code> routines: </p>

<pre>
    require "dtd.pl";
</pre>

<p>All the public routines available are defined within the scope of
package <code>main</code>.  Hence, if you require <code>dtd.pl</code>
in a package other than <code>main</code>, you must use package
qualification when calling a routine.  </p>

<p>Example:</p>
<pre>
    &amp;main'DTDread_dtd(DTD);
</pre>
<p>or,</p>
<pre>
    &amp;'DTDread_dtd(DTD);
</pre>

<p>The following routines are available in <code>dtd.pl</code>:
</p>

<p><strong><a href="#parsing">Parsing Routines</a></strong></p>

<ul>
<li><strong><a href="#DTDread_dtd"
>DTDread_dtd</a></strong>
-- Parse an SGML DTD
</li>
<li><strong><a href="#DTDread_catalog_files"
>DTDread_catalog_files</a></strong>
-- Parse a set of entity map files
</li>
<li><strong><a href="#DTDread_mapfile"
>DTDread_mapfile</a></strong>
-- Parse entity map file
</li>
<li><strong><a href="#DTDreset"
>DTDreset</a></strong>
-- Reset all data structures
</li>
<li><strong><a href="#DTDset_comment_callback"
>DTDset_comment_callback</a></strong>
-- Set SGML comment callback
</li>
<li><strong><a href="#DTDset_debug_callback"
>DTDset_debug_callback</a></strong>
-- Set routine to capture debugging messages
</li>
<li><strong><a href="#DTDset_debug_handle"
>DTDset_debug_handle</a></strong>
-- Set output filehandle for debugging messages
</li>
<li><strong><a href="#DTDset_err_callback"
>DTDset_err_callback</a></strong>
-- Set routine to capture error messages
</li>
<li><strong><a href="#DTDset_err_handle"
>DTDset_err_handle</a></strong>
-- Set output filehandle for error messages
</li>
<li><strong><a href="#DTDset_pi_callback"
>DTDset_pi_callback</a></strong>
-- Set processing instruction callback
</li>
<li><strong><a href="#DTDset_verbosity"
>DTDset_verbosity</a></strong>
-- Set verbosity flag
</li>
</ul>

<p>The following routines are only applicable after <code><a
href="#DTDread_dtd">DTDread_dtd</a></code> has been called.  </p>

<p><strong><a href="#dataaccess">Data Access Routines</a></strong></p>

<ul>
<li><strong><a href="#DTDget_base_children"
>DTDget_base_children</a></strong>
-- Get base elements of an element
</li>
<li><strong><a href="#DTDget_elem_attr"
>DTDget_elem_attr</a></strong>
-- Get attributes for an element
</li>
<li><strong><a href="#DTDget_elements"
>DTDget_elements</a></strong>
-- Get array of all elements
</li>
<li><strong><a href="#DTDget_elements_of_attr"
>DTDget_elements_of_attr</a></strong>
-- Get array of all elements that have a given attribute
</li>
<li><strong><a href="#DTDget_exc_children"
>DTDget_exc_children</a></strong>
-- Get exclusion elements of an element
</li>
<li><strong><a href="#DTDget_gen_ents"
>DTDget_gen_ents</a></strong>
-- Get general entities defined in DTD
</li>
<li><strong><a href="#DTDget_gen_data_ents"
>DTDget_gen_data_ents</a></strong>
-- Get general entities: {PC,C,S}DATA, PI
</li>
<li><strong><a href="#DTDget_inc_children"
>DTDget_inc_children</a></strong>
-- Get inclusion elements of an element
</li>
<li><strong><a href="#DTDget_parents"
>DTDget_parents</a></strong>
-- Get parent elements of an element
</li>
<li><strong><a href="#DTDget_top_elements"
>DTDget_top_elements</a></strong>
-- Get top-most elements
</li>
<li><strong><a href="#DTDis_child"
>DTDis_child</a></strong>
-- Check if element is a child of another element
</li>
<li><strong><a href="#DTDis_element"
>DTDis_element</a></strong>
-- Check if element defined in DTD
</li>
</ul>

<p><strong><a href="#utility">Utility Routines</a></strong></p>

<ul>
<li><strong><a href="#DTDis_attr_keyword"
>DTDis_attr_keyword</a></strong>
-- Check for reserved attribute value
</li>
<li><strong><a href="#DTDis_elem_keyword"
>DTDis_elem_keyword</a></strong>
-- Check for reserved element value
</li>
<li><strong><a href="#DTDis_group_connector"
>DTDis_group_connector</a></strong>
-- Check for group connector
</li>
<li><strong><a href="#DTDis_occur_indicator"
>DTDis_occur_indicator</a></strong>
-- Check for occurrence indicator
</li>
<li><strong><a href="#DTDis_tag_name"
>DTDis_tag_name</a></strong>
-- Check for legal tag name
</li>
<li><strong><a href="#DTDprint_tree"
>DTDprint_tree</a></strong>
-- Output content tree for an element
</li>
<li><strong><a href="#DTDset_tree_callback"
>DTDset_tree_callback</a></strong>
-- Set callback for when a line is to be printed in
<code><a href="#DTDprint_tree">DTDprint_tree</a></code>
</li>
</ul>

<!-- =================================================================== -->
<hr>
<h2><a name="parsing">Parsing Routines</a></h2>

<p>The following routines deal with the parsing of an SGML DTD.  </p>

<h3><a name="DTDread_dtd">DTDread_dtd</a></h3>

<h4>Usage</h4>

<pre>
    $status = &amp;'DTDread_dtd(FILEHANDLE);
</pre>
<h4>Description</h4>

<p><code>DTDread_dtd</code> parses the SGML DTD specified by
<var>FILEHANDLE</var>.
</p>

<dl>
<dt><strong>Note</strong></dt>

<dd>Make sure to package qualify <var>FILEHANDLE</var> when calling
<code>DTDread_dtd</code>.  Otherwise, <var>FILEHANDLE</var> will be
interpreted under the scope of package <code>dtd</code>.  </dd> </dl>

<p>A <code>1</code> is returned if the DTD was successfully parsed.
A <code>0</code> is returned if an error occured.  </p>

<p>Parsing of the DTD stops once the end of the file is
reached, or at the end of the doctype declaration (if a
doctype declaration exists). Any external entity references
will be parsed if an entity to filename mapping exists (see <a
href="#DTDread_mapfile"><code>DTDread_mapfile</code></a>).  </p>

<p><code>DTDread_dtd</code> makes the following assumptions when
parsing a DTD: </p>

<ul>

<li><p>The reference concrete syntax is assumed. However, various
variables in <code>dtd.pl</code> can be redefined to try to accomodate an
alternate syntax. There are some dependencies in the parser on how
certain delimiters are defined. See the Perl source for more
information.
</p></li>

<li><p>The SGML DTD is syntactically correct. This libary is not
intended as a validator. Use <code>nsgmls</code>, or other SGML
validator, for such purposes.  </p></li>

<li><p>The SGML declaration statement is ignored if it exists.
</p></li>

<li><p>Generic identifiers and entity names can only contain the
characters "A-Za-z_.-".  However, this can be changed by setting
the variable <code>$namechars</code>.  There is no size limit on
name length.  </p></li>

<li><p>Element names are treated with case-insensitivity, but entity
names are case-sensitive. Tag names are converted and stored in
lowercase.  </p></li>

<li><p>Multiple contiguous whitespaces are ignored in entity
identifiers.  I.e. Multiple contiguous whitespaces are treated as
one whitespace character.  </p></li>

</ul>

<p>After <code>DTDread_dtd</code> is finished, the following variables
are filled (Note: all the variables are within the scope of package
dtd): </p>

<dl>
<dt><code>@ParEntities</code></dt>

    <dd>Parameter entities in order processed</dd>

<dt><code>@GenEntities</code></dt>

    <dd>General entities in order processed</dd>

<dt><code>@Elements</code></dt>

    <dd>Elements in order processed</dd>

<dt><code>%ParEntity</code></dt>

    <dd><em>Keys</em>: Non-external parameter entities.<br>
    <em>Values</em>: Replacement value.</dd>

<dt><code>%PubParEntity</code></dt>

    <dd><em>Keys</em>: External public parameter entities (PUBLIC).<br>
    <em>Values</em>: Entity identifier, if defined.</dd>

<dt><code>%SysParEntity</code></dt>

    <dd><em>Keys</em>: External public parameter entities (SYSTEM).<br>
    <em>Values</em>: Entity identifier, if defined.</dd>

<dt><code>%GenEntity</code></dt>

    <dd><em>Keys</em>: Regular general entities.<br>
    <em>Values</em>: Entity value.</dd>

<dt><code>%StartTagEntity</code></dt>

    <dd><em>Keys</em>: STARTTAG general entities.<br>
    <em>Values</em>: Entity value.</dd>

<dt><code>%EndTagEntity</code></dt>

    <dd><em>Keys</em>: ENDTAG general entities.<br>
    <em>Values</em>: Entity value.</dd>

<dt><code>%MSEntity</code></dt>

    <dd><em>Keys</em>: MS general entities.<br>
    <em>Values</em>: Entity value.</dd>

<dt><code>%MDEntity</code></dt>

    <dd><em>Keys</em>: MD general entities.<br>
    <em>Values</em>: Entity value.</dd>

<dt><code>%PIEntity</code></dt>

    <dd><em>Keys</em>: PI general entities.<br>
    <em>Values</em>: Entity value.</dd>

<dt><code>%CDataEntity</code></dt>

    <dd><em>Keys</em>: CDATA general entities.<br>
    <em>Values</em>: Entity value.</dd>

<dt><code>%SDataEntity</code></dt>

    <dd><em>Keys</em>: SDATA general entities.<br>
    <em>Values</em>: Entity value.</dd>

<dt><code>%ElemCont</code></dt>

    <dd><em>Keys</em>: Element names.<br>
    <em>Values</em>: Base content of declaration of elements.</dd>

<dt><code>%ElemInc</code></dt>

    <dd><em>Keys</em>: Element names.<br>
    <em>Values</em>: Inclusion set declarations.</dd>

<dt><code>%ElemExc</code></dt>

    <dd><em>Keys</em>: Element names.<br>
    <em>Values</em>: Exclusion set declarations.</dd>

<dt><code>%ElemTag</code></dt>

    <dd><em>Keys</em>: Element names.<br>
    <em>Values</em>: Omitted tag minimization.</dd>

<dt><code>%Attribute</code></dt>

    <dd><em>Keys</em>: Element names.<br>
    <em>Values</em>: Attributes for elements. To access the data stored in
    <code>%Attribute</code>, it is best to use
    <a href="#DTDget_elem_attr"><code>DTDget_elem_attr</code></a>.
    </dd>

<dt><code>%PubNotation</code></dt>

    <dd><em>Keys</em>: PUBLIC Notation names.<br>
    <em>Values</em>: Notation identifier.</dd>

<dt><code>%SysNotation</code></dt>

    <dd><em>Keys</em>: SYSTEM Notation names.<br>
    <em>Values</em>: Notation identifier.</dd>

<dt><code>%ElemsOfAttr</code></dt>

    <dd><em>Keys</em>: Attribute names.<br>
    <em>Values</em>: A <code>$;</code> list of elements that have
    the key as an attribute.</dd>

</dl>

<p>All entities are expanded when data is stored in
<code>%ElemCont</code>, <code>%ElemInc</code>, <code>%ElemInc</code>,
<code>%ElemExc</code>, <code>%ElemTag</code>, <code>%Attribute</code>
arrays.  </p>

<p>To avoid maintenance problems with programs directly accessing the
variables set by <code>DTDread_dtd</code>, <code>dtd.pl</code> defines
<a href="#dataaccess">routines</a> to access the data contained in
the variables.  If you use <code>dtd.pl</code>, try to use the <a
href="#dataaccess">data access routines</a> when at all possible.  </p>

<h4>Notes</h4>

<ul>

    <li><p>External PUBLIC and SYSTEM general and data entities are
    ignored.  </p>
    </li>
    <li><p>Concurrent DTDs are not distinguished.  </p>
    </li>
    <li><p>LINKTYPE, SHORTREF, USEMAP declarations are ignored.  </p>
    </li>
    <li><p>Data attribute declarations (ie. "&lt;!ATTLIST #NOTATION ...)
    are ignored.  </p>
    </li>
    <li><p><code>DTDread_dtd</code>'s performance is not the best.
    <code>DTDread_dtd</code> makes frequent use of Perl's <code>getc</code>
    function.  </p>
    </li>

</ul>


<h3><a name="DTDread_catalog_files">DTDread_catalog_files</a></h3>

<h4>Usage</h4>

<pre>
    &amp;'DTDread_catalog_files(@files);
</pre>

<h4>Description</h4>

<p><code>DTDread_catalog_files</code> reads all catalog
files specified by <code>@files</code> and by the <a
href="#SGML_CATALOG_FILES">SGML_CATALOG_FILES</a> envariable. </p>

<!--	@(#)  catalog.mod 1.4 96/10/07 @(#)
  -->
<p><strong>Catalog Syntax</strong></p>

<p>The syntax of a catalog is a subset of SGML catalogs
(as defined in
<cite>SGML Open Draft Technical Resolution 9401:1994</cite>).
</p>

<p>A catalog contains a sequence of the following types of entries:
</p>

<dl>
<dt><code>PUBLIC</code> <var>public_id</var> <var>system_id</var></dt>
<dd><p>This maps <var>public_id</var> to <var>system_id</var>.
</p>
</dd>
<dt><code>ENTITY</code> <var>name</var> <var>system_id</var></dt>
<dd><p>This maps a general entity whose name is <var>name</var> to
<var>system_id</var>.
</p>
</dd>
<dt><code>ENTITY %</code><var>name</var> <var>system_id</var></dt>
<dd><p>This maps a parameter entity whose name is <var>name</var> to
<var>system_id</var>.
</p>
</dd>
</dl>

<p><strong>Syntax Notes</strong></p>

<ul>
<li><p>A <var>system_id</var> string cannot contain any spaces.  The
<var>system_id</var> is treated as pathname of file. </p>
</li>
<li><p>Any line in a catalog file that does not follow the previously
mentioned entries is ignored.</p>
</li>
<li><p>In case of duplicate entries, the first entry defined is used.
</ul>

<p>Example catalog file:</p>
<pre>
        -- ISO public identifiers --
PUBLIC "ISO 8879-1986//ENTITIES General Technical//EN"            iso-tech.ent
PUBLIC "ISO 8879-1986//ENTITIES Publishing//EN"                   iso-pub.ent
PUBLIC "ISO 8879-1986//ENTITIES Numeric and Special Graphic//EN"  iso-num.ent
PUBLIC "ISO 8879-1986//ENTITIES Greek Letters//EN"                iso-grk1.ent
PUBLIC "ISO 8879-1986//ENTITIES Diacritical Marks//EN"            iso-dia.ent
PUBLIC "ISO 8879-1986//ENTITIES Added Latin 1//EN"                iso-lat1.ent
PUBLIC "ISO 8879-1986//ENTITIES Greek Symbols//EN"                iso-grk3.ent 
PUBLIC "ISO 8879-1986//ENTITIES Added Latin 2//EN"                ISOlat2
PUBLIC "ISO 8879-1986//ENTITIES Added Math Symbols: Ordinary//EN" ISOamso

        -- HTML public identifiers and entities --
PUBLIC "-//IETF//DTD HTML//EN"                                    html.dtd
PUBLIC "ISO 8879-1986//ENTITIES Added Latin 1//EN//HTML"          ISOlat1.ent
ENTITY "%html-0"                                                  html-0.dtd
ENTITY "%html-1"                                                  html-1.dtd

</pre>

<p><strong>Environment Variables</strong></p>

<p>The following
envariables (ie. environment variables) are supported:
</p>

<dl>
<dt><a name="P_SGML_PATH">P_SGML_PATH</a></dt>
<dd><p>This is a colon (semi-colon for MSDOS users)
separated list of paths for finding catalog files
or system identifiers.  For example, if a system identifier is not
an absolute pathname, then the paths listed in P_SGML_PATH are used to
find the file.
</p>
</dd>
<dt><a name="SGML_CATALOG_FILES">SGML_CATALOG_FILES</a></dt>
<dd><p>This envariable is a colon (semi-colon for MSDOS users)
separated list of catalog files to read.
If
a file in the list is not an absolute path, then file is searched in
the paths listed in the P_SGML_PATH and SGML_SEARCH_PATH.
</p>
</dd>
<dt><a name="SGML_SEARCH_PATH">SGML_SEARCH_PATH</a></dt>
<dd><p>This is a colon (semi-colon for MSDOS users)
separated list of paths for finding catalog files
or system identifiers.  This envariable serves the same function as
P_SGML_PATH.  If both are defined, paths listed in P_SGML_PATH are
searched first before any paths in SGML_SEARCH_PATH.</p>
</dd>
</dl>
<p>The use of P_SGML_PATH is for compatibility with earlier versions.
SGML_CATALOG_FILES and SGML_SEARCH_PATH
are supported for compatibility with James Clark's <code>nsgmls(1)</code>.
</p>
<dl>
<dt><strong>Note</strong></dt>
<dd>When searching for a file via the P_SGML_PATH and/or SGML_SEARCH_PATH,
if the file is not found in any of the paths, then the current working
directory is searched.
</dd>
</dl>



<h3><a name="DTDread_mapfile">DTDread_mapfile</a></h3>

<h4>Usage</h4>

<pre>
    &amp;'DTDread_mapfile($filename);
</pre>

<h4>Description</h4>

<p><code>DTDread_mapfile</code> parses a catalog specified
<code>$filename</code>.  </p>

<p>This function is similiar to <a
href="#DTDread_catalog_files"><code>DTDread_catalog_files</code></a>
with the exception only <code>$filename</code> is read.  </p>

<h3><a name="DTDreset">DTDreset</a></h3>

<h4>Usage</h4>

<pre>
    &amp;'DTDreset();
</pre>

<h4>Description</h4>

<p><code>DTDreset</code> clears all data associated with the DTD read
via <a href="#DTDread_dtd"><code>DTDread_dtd</code></a>.  This routine
is useful if multiple DTDs need to be processed.  </p>

<h3><a name="DTDset_comment_callback">DTDset_comment_callback</a></h3>

<h4>Usage</h4>

<pre>
    &amp;'DTDset_comment_callback($callback);
</pre>

<h4>Description</h4>

<p><code>DTDset_comment_callback</code>
sets the function,
<code>$callback</code>,
to be called
when a comment declaration is read during
<a href="#DTDread_dtd"><code>DTDread_dtd</code></a>.
<code>$callback</code>
is called as follows:
</p>

<pre>
    &amp;$callback(*comment_text);
</pre>

<p><code>*comment_text</code> is a pointer to the string containing all
the text within the SGML comment declaration (excluding the open and close
delimiters).
</p>

<dl>
<dt><strong>Note</strong></dt>

    <dd><p>Make sure to package qualify the callback; otherwise, the
    callback will be invoked within the scope of package <code>dtd</code>.
    </p></dd>
</dl>


<h3><a name="DTDset_debug_callback">DTDset_debug_callback</a></h3>

<h4>Usage</h4>

<pre>
    &amp;'DTDset_debug_callback($callback);
</pre>

<h4>Description</h4>

<p><code>DTDset_debug_callback</code>
sets the function,
<code>$callback</code>,
to be called
when a debugging message is generated during
<a href="#DTDread_dtd"><code>DTDread_dtd</code></a>.
<code>$callback</code>
is called as follows:
</p>

<pre>
    &amp;$callback($message);
</pre>

<p><code>$message</code> is a string containing the debugging message.
The callback will only be invoked if verbosity is set via
<code><a href="#DTDset_verbosity">DTDset_verbosity</a></code>.
If a debugging callback is registered, then debugging messages will
be supressed from standard error or the filehandle registered via
the <code><a href="#DTDset_debug_handle">DTDset_debug_handle</a></code>.
</p>

<dl>
<dt><strong>Note</strong></dt>

    <dd><p>Make sure to package qualify the callback; otherwise, the
    callback will be invoked within the scope of package <code>dtd</code>.
    </p></dd>
</dl>


<h3><a name="DTDset_debug_handle">DTDset_debug_handle</a></h3>

<h4>Usage</h4>

<pre>
    &amp;'DTDset_debug_handle(<var>FILEHANDLE</var>);
</pre>

<h4>Description</h4>

<p><code>DTDset_debug_handle</code>
sets the filehandle to send all debugging messages generated
during
<a href="#DTDread_dtd"><code>DTDread_dtd</code></a>.
The default filehandle is "<code>STDERR</code>".
</p>

<p>Messages will be generated only if verbosity is set via
<code><a href="#DTDset_verbosity">DTDset_verbosity</a></code>.
If a debugging callback is registered via
<code><a href="#DTDset_debug_callback">DTDset_debug_callback</a></code>.
then debugging messages will
be supressed from the filehandle.
</p>

<dl>
<dt><strong>Note</strong></dt>

    <dd><p>Make sure to package qualify the filehandle; otherwise, the
    filehandle will be interpreted within the scope of package <code>dtd</code>.
    </p></dd>
</dl>

<h3><a name="DTDset_err_callback">DTDset_err_callback</a></h3>

<h4>Usage</h4>

<pre>
    &amp;'DTDset_err_callback($callback);
</pre>

<h4>Description</h4>

<p><code>DTDset_err_callback</code>
sets the function,
<code>$callback</code>,
to be called
when an error message is generated during
<a href="#DTDread_dtd"><code>DTDread_dtd</code></a>.
<code>$callback</code>
is called as follows:
</p>

<pre>
    &amp;$callback($message);
</pre>

<p><code>$message</code> is a string containing the error message.
The callback will only be invoked if verbosity is set via
<code><a href="#DTDset_verbosity">DTDset_verbosity</a></code>.
If a error callback is registered, then error messages will
be supressed from standard error or the filehandle registered via
the <code><a href="#DTDset_err_handle">DTDset_err_handle</a></code>.
</p>

<dl>
<dt><strong>Note</strong></dt>

    <dd><p>Make sure to package qualify the callback; otherwise, the
    callback will be invoked within the scope of package <code>dtd</code>.
    </p></dd>
</dl>


<h3><a name="DTDset_err_handle">DTDset_err_handle</a></h3>

<h4>Usage</h4>

<pre>
    &amp;'DTDset_err_handle(<var>FILEHANDLE</var>);
</pre>

<h4>Description</h4>

<p><code>DTDset_err_handle</code>
sets the filehandle to send all error messages generated
<a href="#DTDread_dtd"><code>DTDread_dtd</code></a>.
The default filehandle is "<code>STDERR</code>".
</p>

<p>Messages will be generated only if verbosity is set via
<code><a href="#DTDset_verbosity">DTDset_verbosity</a></code>.
If a error callback is registered via
<code><a href="#DTDset_err_callback">DTDset_err_callback</a></code>.
then error messages will
be supressed from the filehandle.
</p>

<dl>
<dt><strong>Note</strong></dt>

    <dd><p>Make sure to package qualify the filehandle; otherwise,
    the filehandle will be interpreted within the scope of package
    <code>dtd</code>.  </p></dd>
</dl>

<h3><a name="DTDset_pi_callback">DTDset_pi_callback</a></h3>

<h4>Usage</h4>

<pre>
    &amp;'DTDset_pi_callback($callback);
</pre>

<h4>Description</h4>

<p><code>DTDset_pi_callback</code>
sets the function,
<code>$callback</code>,
to be called when a
processing instruction is read during
<a href="#DTDread_dtd"><code>DTDread_dtd</code></a>.
<code>$callback</code>
is called as follows:
</p>

<pre>
    &amp;$callback(*pi_text);
</pre>

<p><code>*pi_text</code>
is a pointer to the string containing all the text within the
processing instruction (excluding the open and close delimiters).
</p>

<dl>
<dt><strong>Note</strong></dt>

    <dd><p>Make sure to package qualify the callback; otherwise, the
    callback will be invoked within the scope of package <code>dtd</code>.
    </p></dd>
</dl>


<h3><a name="DTDset_verbosity">DTDset_verbosity</a></h3>

<h4>Usage</h4>

<pre>
    &amp;'DTDset_verbosity($value);
</pre>

<h4>Description</h4>

<p><code>DTDset_verbosity</code> sets the verbosity flag
for <a href="#DTDread_dtd"><code>DTDread_dtd</code></a>.
If <code>$value</code> is non-zero, then <a
href="#DTDread_dtd"><code>DTDread_dtd</code></a> outputs status
messages as it parses a DTD.  This function is used for debugging
purposes.  </p>

<!-- =================================================================== -->
<hr>
<h2><a name="dataaccess">Data Access Routines</a></h2>

<p>The following routines access the data
extracted from an SGML DTD via
<a href="#DTDread_dtd"><code>DTDread_dtd</code></a>
</p>

<h3><a name="DTDget_elements">DTDget_elements</a></h3>

<h4>Usage</h4>

<pre>
    @elements = &amp;'DTDget_elements();
    @elements = &amp;'DTDget_elements($nosortflag);
</pre>

<h4>Description</h4>

<p><code>DTDget_elements</code>
retrieves an array of all elements defined in
the DTD.
An optional flag argument can be passed to the routine to
determine is elements returned are sorted or not: 0 =&gt; sorted,
1 =&gt; not sorted.
</p>

<h3><a name="DTDget_elements_of_attr">DTDget_elements_of_attr</a></h3>

<h4>Usage</h4>

<pre>
    @elements = &amp;'DTDget_elements_of_attr($attribute_name);
</pre>

<h4>Description</h4>
<p><code>DTDget_elements_of_attr</code>
retrieves an array of all elements that contain the specified
attribute.
</p>

<h3><a name="DTDget_top_elements">DTDget_top_elements</a></h3>

<h4>Usage</h4>

<pre>
    @top_elements = &amp;'DTDget_elements();
</pre>

<h4>Description</h4>

<p><code>DTDget_top_elements</code>
retrieves a sorted array of all top-most elements
defined in the DTD. Top-most elements are those <em>elements that cannot
be contained within another element or can only be contained within
itself</em>.
</p>

<h3><a name="DTDget_elem_attr">DTDget_elem_attr</a></h3>

<h4>Usage</h4>

<pre>
    %attribute = &amp;'DTDget_elem_attr($elem);
</pre>

<h4>Description</h4>

<p><code>DTDget_elem_attr</code>
returns an associative array containing the
attributes of
<code>$elem</code>.
The keys of the array are the attribute names,
and the array values are
<code>$;</code>
separated strings of the possible values
for the attributes. Example of extracting an attribute's values:
</p>

<pre>
    @values = split(/$;/, $attribute{`alignment'});
</pre>

<p>The first array value of the
<code>$;</code>
splitted array is the default value
for the attribute (which may be an SGML reserved word). If the default
value equals
"<code>#FIXED</code>",
then the next array value is the
<code>#FIXED</code>
value.
The other array values are all possible values for the attribute.
</p>

<dl>
<dt><strong>Note</strong></dt>

    <dd><p><code>$;</code> is assumed to be the default value assigned
    by Perl: "\034".  If <code>$;</code> is changed, unpredictable
    results may occur.  </p></dd>
</dl>

<h3><a name="DTDget_parents">DTDget_parents</a></h3>

<h4>Usage</h4>

<pre>
    @parent_elements = &amp;'DTDget_parents($elem);
</pre>

<h4>Description</h4>

<p><code>DTDget_parents</code> returns an array of all elements that
may be a parent of <code>$elem</code>.  </p>


<h3><a name="DTDget_base_children">DTDget_base_children</a></h3>

<h4>Usage</h4>

<pre>
    @base_children = &amp;'DTDget_base_children($elem, $andcon);
</pre>

<h4>Description</h4>

<p><code>DTDget_base_children</code>
returns an array of the elements in the base
model group of
<code>$elem</code>.
The
<code>$andcon</code>
is flag if the connector characters
are included in the returned array: 0 =&gt; no connectors, 1 (non-zero)
=&gt; connectors.
</p>

<p>Example:</p>

<pre>
    &lt;!ELEMENT foo (x | y | z) +(a | b) -(m | n)&gt;
</pre>

<p>The call</p>

<pre>
    &amp;'DTDget_base_children(`foo')
</pre>

<p>will return</p>

<pre>
    (`x', `y', `z')
</pre>

<p>The call</p>

<pre>
    &amp;'DTDget_base_children(`foo', 1)
</pre>

<p>will return</p>

<pre>
    (`(`,`x', `|', `y', `|', `z', `)')
</pre>

<p>One may use
<a href="#DTDis_tag_name"><code>DTDis_tag_name</code></a>
to distinguish
elements from the connectors.
</p>


<h3><a name="DTDget_exc_children">DTDget_exc_children</a></h3>

<h4>Usage</h4>

<pre>
    @exc_children = &amp;'DTDget_exc_children($elem, $andcon);
</pre>

<h4>Description</h4>

<p><code>DTDget_exc_children</code>
returns an array of the elements in the exclusion
model group of
<code>$elem</code>.
The
<code>$andcon</code>
is flag if the connector characters
are included in the returned array: 0 =&gt; no connectors, 1 (non-zero)
=&gt; connectors.
</p>

<p>Example:</p>

<pre>
    &lt;!ELEMENT foo (x | y | z) +(a | b) -(m | n)&gt;
</pre>

<p>The call</p>

<pre>
    &amp;'DTDget_exc_children(`foo')
</pre>

<p>will return</p>

<pre>
    (`m', `n')
</pre>

<h3><a name="DTDget_gen_ents">DTDget_gen_ents</a></h3>

<h4>Usage</h4>

<pre>
    @generalents = &amp;'DTDget_gen_ents();
    @generalents = &amp;'DTDget_gen_ents($nosort);
</pre>

<h4>Description</h4>

<p><code>DTDget_gen_ents</code>
returns an array of general entities.
An optional flag argument can be passed to the routine to
determine is elements returned are sorted or not: 0 => sorted,
1 => not sorted.
</p>

<h3><a name="DTDget_gen_data_ents">DTDget_gen_data_ents</a></h3>

<h4>Usage</h4>

<pre>
    @gendataents = &amp;'DTDget_gen_data_ents();
</pre>

<h4>Description</h4>

<p><code>DTDget_gen_data_ents</code>
returns an array of general data
entities defined in the DTD.  Data entities cover the
following: PCDATA, CDATA, SDATA, PI.
</p>


<h3><a name="DTDget_inc_children">DTDget_inc_children</a></h3>

<h4>Usage</h4>

<pre>
    @inc_children = &amp;'DTDget_inc_children($elem, $andcon);
</pre>

<h4>Description</h4>

<p><code>DTDget_inc_children</code>
returns an array of the elements in the inclusion
model group of
<code>$elem</code>.
The
<code>$andcon</code>
is flag if the connector characters
are included in the returned array: 0 =&gt; no connectors, 1 (non-zero)
=&gt; connectors.
</p>

<p>Example:</p>

<pre>
    &lt;!ELEMENT foo (x | y | z) +(a | b) -(m | n)&gt;
</pre>

<p>The call</p>

<pre>
    &amp;'DTDget_inc_children(`foo')
</pre>

<p>will return</p>

<pre>
    (`a', `b')
</pre>

<h3><a name="DTDis_element">DTDis_element</a></h3>

<h4>Usage</h4>

<pre>
    &amp;'DTDis_element($element);
</pre>

<h4>Description</h4>

<p><code>DTDis_element</code>
returns 1 if
<code>$element</code>
is defined in the DTD. Otherwise,
0 is returned.
</p>

<h3><a name="DTDis_child">DTDis_child</a></h3>

<h4>Usage</h4>

<pre>
    &amp;'DTDis_child($element, $child);
</pre>

<h4>Description</h4>

<p><code>DTDis_child</code>
returns 1 if
<code>$child</code> can be a legal child of
<code>$element</code>
Otherwise, 0 is returned.
</p>

<!-- =================================================================== -->
<hr>
<h2><a name="utility">Utility Routines</a></h2>

<p>The following are general utility routines.
</p>

<h3><a name="DTDis_attr_keyword">DTDis_attr_keyword</a></h3>

<h4>Usage</h4>
<pre>
    &amp;'DTDis_attr_keyword($word);
</pre>

<h4>Description</h4>

<p><code>DTDis_attr_keyword</code>
returns 1 if
<code>$word</code>
is an attribute content reserved
value, otherwise, it returns 0. In the reference concrete syntax, the
following values of
<code>$word</code>
will return 1:
</p>

<ul>
    <li>CDATA</li>
    <li>ENTITY</li>
    <li>ENTITIES</li>
    <li>ID</li>
    <li>IDREF</li>
    <li>IDREFS</li>
    <li>NAME</li>
    <li>NAMES</li>
    <li>NMTOKEN</li>
    <li>NMTOKENS</li>
    <li>NOTATION</li>
    <li>NUMBER</li>
    <li>NUMBERS</li>
    <li>NUTOKEN</li>
    <li>NUTOKENS</li>
</ul>

<p>Character case is ignored.  </p>


<h3><a name="DTDis_elem_keyword">DTDis_elem_keyword</a></h3>

<h4>Usage</h4>

<pre>
    &amp;'DTDis_elem_keyword($word);
</pre>

<h4>Description</h4>

<p><code>DTDis_elem_keyword</code>
returns 1 if
<code>$word</code>
is an element content reserved
value, otherwise, it returns 0. In the reference concrete syntax, the
following values of
<code>$word</code>
will return 1:
</p>

<ul>
    <li>#PCDATA</li>
    <li>CDATA</li>
    <li>EMPTY</li>
    <li>RCDATA</li>
</ul>

<p>Character case is ignored.  </p>

<h3><a name="DTDis_group_connector">DTDis_group_connector</a></h3>

<h4>Usage</h4>

<pre>
    &amp;'DTDis_group_connector($char);
</pre>

<h4>Description</h4>

<p><code>DTDis_group_connector</code>
returns 1 if
<code>$char</code>
is an group connector,
otherwise, it returns 0. The following values of
<code>$char</code>
will return 1:
</p>

<ul>
    <li>,</li>
    <li>&amp;</li>
    <li>|</li>
</ul>

<h3><a name="DTDis_occur_indicator">DTDis_occur_indicator</a></h3>

<h4>Usage</h4>

<pre>
    &amp;'DTDis_occur_indicator($char);
</pre>

<h4>Description</h4>

<p><code>DTDis_occur_indicator</code>
returns 1 if
<code>$char</code>
is an occurence indicator,
otherwise, it returns 0. The following values of
<code>$char</code>
will return 1:
</p>

<ul>
    <li>+</li>
    <li>?</li>
    <li>*</li>
</ul>

<h3><a name="DTDis_tag_name">DTDis_tag_name</a></h3>

<h4>Usage</h4>

<pre>
    &amp;'DTDis_tag_name($string);
</pre>

<h4>Description</h4>

<p><code>DTDis_tag_name</code>
returns 1 if
<code>$string</code>
is a legal tag name, otherwise, it
returns 0. Legal characters in a tag name are defined by the
<code>$namechars</code>
variable. By default, a tag name may only contain the
characters "A-Za-z_.-".
</p>

<h3><a name="DTDprint_tree">DTDprint_tree</a></h3>

<h4>Usage</h4>

<pre>
    &amp;'DTDprint_tree($elem, $depth, FILEHANDLE);
</pre>

<h4>Description</h4>

<p><code>DTDprint_tree</code>
prints the content hierarchy of a single element,
<code>$elem</code>,
to a maximum depth of
<code>$depth</code>
to the file specified by
<var>FILEHANDLE</var>.
If
<var>FILEHANDLE</var>
is not specified then output goes to standard out. A depth of 5
is used if
<code>$depth</code>
is not specified. The root of the tree has a depth
of 1.
</p>

<!--	@(#)  tree.mod 1.3 96/10/06 @(#)
  -->

<p>The tree shows the overall content hierarchy for an element.
Content hierarchies of descendents will also be shown.  Elements that
exist at a higher (or equal) level, or if the maximum depth has been
reached, are pruned.  The string "<code>...</code>" is appended to an
element if it has been pruned due to pre-existance at a higher (or
equal) level.  The content of the pruned element can be determined
by searching for the complete tree of the element (ie. elements w/o
"<code>...</code>").  Elements pruned because maximum depth has been
reached will not have "<code>...</code>" appended.

</p>

<p>Example:
</p>

<pre>
     |__section+)
         |_(effect?, ...
         |__title, ...
         |__toc?, ...
         |__epc-fig*,
         |   |_(effect?, ...
         |   |__figure,
         |   |   |_(effect?, ...
         |   |   |__title, ...
         |   |   |__graphic+, ...
         |   |   |__assoc-text?)
</pre>

<dl>
<dt><strong>Note</strong></dt>
<dd><p>Pruning must be done to avoid a combinatorical explosion.
It is common for DTD's to define content hierarchies of infinite
depth.  Even with a predefined maximum depth, the generated tree
can become very large.
</p>
</dd>
</dl>

<p>Since the tree outputed is static, the inclusion and exclusion sets
of elements are treated specially. Inclusion and exclusion elements
inherited from ancestors are not propagated down to determine
what elements are printed, but special markup is presented at a
given element if there exists inclusion and exclusion elements from
ancestors. The reason inclusions and exclusions are not propagated down
is because of the pruning done. Since an element may occur in multiple
contexts -- and have different ancestoral inclusions and exclusions in
effect -- an element without "<code>...</code>" may be the only place
of reference to see the content hierarchy of the element.

</p>

<p>Example:</p>

<pre>
    D1
     |  {+} idx needbegin needend newline
     | 
     |_(head,
     |   | {A+} idx needbegin needend newline
     |   |  {-} needbegin needend
     |   | 
     |   |_(((#PCDATA |
     |   |____((acro |
     |   |       | {A+} idx needbegin needend newline
     |   |       | {A-} needbegin needend
     |   |       | 
     |   |       |_(((#PCDATA |
     |   |       |____((super | ...
     |   |       |______sub)))*)) ...
</pre>

<p>Ignoring the lines starting with {}'s, one gets the content
hierachy of an element as defined by the DTD without concern of where
it may occur in the overall structure. The {} lines give additional
information regarding the element with respect to its existance
within a specific context. For example, when an <code>ACRO</code>
element occurs within <code>D1,HEAD</code> -- along with its normal
content -- it can contain <code>IDX</code> and <code>NEWLINE</code>
elements due to inclusions from ancestors. However, it cannot contain
<code>NEEDBEGIN</code> and <code>NEEDEND</code> regardless of its
defined content since an ancestor(s) excludes them.

</p>

<dl>
<dt><strong>Note</strong></dt>
<dd>Exclusions override inclusions. If an element occurs in an
inclusion set and an exclusion set, the exclusion takes
precedence. Therefore, in the above example, <code>NEEDBEGIN</code>, 
<code>NEEDEND</code> are excluded from <code>ACRO</code>.</dd>
</dl>

<p>Explanation of {}'s keys:
</p>
<dl>
<dt><code>{+}</code></dt>
<dd>The list of inclusion elements defined by the current element.
Since this is part of the content model of the element, the
inclusion subelements are printed as part of the content
hierarchy of the current element after the base content model.
Subelements that are inclusions will have <code>{+}</code> appended
to the subelement entry.
</dd>
<dt><code>{A+}</code></dt>
<dd>The list of inclusion elements due to ancestors. This is listed
as reference to determine the content of an element within a
given context. None of the ancestoral inclusion elements are
printed as part of the content hierarchy of the element. 
</dd>
<dt><code>{-}</code></dt>
<dd>The list of exclusion elements defined by the current
element. Since this is part of the content model of the
element, any subelement in the content model that would be
excluded will have <code>{-}</code> appended to the subelement
listing.
</dd>
<dt><code>{A-}</code></dt>
<dd>The list of exclusion elements due to ancestors. This is listed
as reference to determine the content of an element within a
given context. None of the ancestoral exclusion elements
have any effect on the printing of the content hierarchy of
the current element.
</dd>
</dl>


<h3><a name="DTDset_tree_callback">DTDset_tree_callback</a></h3>

<h4>Usage</h4>

<pre>
    &amp;'DTDset_tree_callback($callback);
</pre>

<h4>Description</h4>

<p><code>DTDset_tree_callback</code>
sets the function,
<code>$callback</code>,
to be called
when a line of output is generated via
<a href="#DTDprint_tree"><code>DTDprint_tree</code></a>.
<code>$callback</code>
is called as follows:
</p>

<pre>
    $cb_return = &amp;$callback($line);
</pre>

<p>The return value of the callback will be the actual text that gets
outputed by
<a href="#DTDprint_tree"><code>DTDprint_tree</code></a>.
</p>

<dl>
<dt><strong>Note</strong></dt>

    <dd><p>Make sure to package qualify the callback; otherwise, the
    callback will be invoked within the scope of package <code>dtd</code>.
    </p></dd>
</dl>


<!-- =================================================================== -->
<!--	@(#)  avail.mod 1.1 96/09/30 @(#)
  -->
<hr>
<h2><a name="availability">Availability</a></h2>
<p>This program is part of the <em>perlSGML</em> package; see
&lt;URL:<a href="file:/usr/doc/perlsgml/perlSGML.html"
>file:/usr/doc/perlsgml/perlSGML.html</a>&gt;
</p>

<!--	@(#)  author.mod 1.1 96/09/30 @(#)
  -->
<hr>
<h2><a name="author">Author</a></h2>
<address>
<a href="http://www.oac.uci.edu/indiv/hood">Earl Hood</a>
&lt;<a href="mailto:ehood@medusa.acs.uci.edu"
>ehood@medusa.acs.uci.edu</a>&gt;<br>
</address>

<!-- =================================================================== -->
<hr>
</body>
</html>