aboutsummaryrefslogtreecommitdiff
path: root/doc/lua-filters.md
blob: c5f7d2713057a4ff26f64c03cb20f05bba8c73fe (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
3079
3080
3081
3082
3083
3084
3085
3086
3087
3088
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
3147
3148
3149
3150
3151
3152
3153
3154
3155
3156
3157
3158
3159
3160
3161
3162
3163
3164
3165
3166
3167
3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
3180
3181
3182
3183
3184
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194
3195
3196
3197
3198
3199
3200
3201
3202
3203
3204
3205
3206
3207
3208
3209
3210
3211
3212
3213
3214
3215
3216
3217
3218
3219
3220
3221
3222
3223
3224
3225
3226
3227
3228
3229
3230
3231
3232
3233
3234
3235
3236
3237
3238
3239
3240
3241
3242
3243
3244
---
author:
- Albert Krewinkel
- John MacFarlane
date: 'January 10, 2020'
title: Pandoc Lua Filters
---

# Introduction

Pandoc has long supported filters, which allow the pandoc
abstract syntax tree (AST) to be manipulated between the parsing
and the writing phase. [Traditional pandoc
filters](https://pandoc.org/filters.html) accept a JSON
representation of the pandoc AST and produce an altered JSON
representation of the AST. They may be written in any
programming language, and invoked from pandoc using the
`--filter` option.

Although traditional filters are very flexible, they have a
couple of disadvantages. First, there is some overhead in
writing JSON to stdout and reading it from stdin (twice, once on
each side of the filter). Second, whether a filter will work
will depend on details of the user's environment. A filter may
require an interpreter for a certain programming language to be
available, as well as a library for manipulating the pandoc AST
in JSON form. One cannot simply provide a filter that can be
used by anyone who has a certain version of the pandoc
executable.

Starting with version 2.0, pandoc makes it possible to write
filters in Lua without any external dependencies at all. A Lua
interpreter (version 5.3) and a Lua library for creating pandoc
filters is built into the pandoc executable. Pandoc data types
are marshalled to Lua directly, avoiding the overhead of writing
JSON to stdout and reading it from stdin.

Here is an example of a Lua filter that converts strong emphasis
to small caps:

``` lua
return {
  {
    Strong = function (elem)
      return pandoc.SmallCaps(elem.c)
    end,
  }
}
```

or equivalently,

``` lua
function Strong(elem)
  return pandoc.SmallCaps(elem.c)
end
```

This says: walk the AST, and when you find a Strong element,
replace it with a SmallCaps element with the same content.

To run it, save it in a file, say `smallcaps.lua`, and invoke
pandoc with `--lua-filter=smallcaps.lua`.

Here's a quick performance comparison, converting the pandoc
manual (MANUAL.txt) to HTML, with versions of the same JSON
filter written in compiled Haskell (`smallcaps`) and interpreted
Python (`smallcaps.py`):

  Command                                 Time
  --------------------------------------- -------
  `pandoc`                                1.01s
  `pandoc --filter ./smallcaps`           1.36s
  `pandoc --filter ./smallcaps.py`        1.40s
  `pandoc --lua-filter ./smallcaps.lua`   1.03s

As you can see, the Lua filter avoids the substantial overhead
associated with marshalling to and from JSON over a pipe.

# Lua filter structure

Lua filters are tables with element names as keys and values
consisting of functions acting on those elements.

Filters are expected to be put into separate files and are
passed via the `--lua-filter` command-line argument. For
example, if a filter is defined in a file `current-date.lua`,
then it would be applied like this:

    pandoc --lua-filter=current-date.lua -f markdown MANUAL.txt

The `--lua-filter` option may be supplied multiple times. Pandoc
applies all filters (including JSON filters specified via
`--filter` and Lua filters specified via `--lua-filter`) in the
order they appear on the command line.

Pandoc expects each Lua file to return a list of filters. The
filters in that list are called sequentially, each on the result
of the previous filter. If there is no value returned by the
filter script, then pandoc will try to generate a single filter
by collecting all top-level functions whose names correspond to
those of pandoc elements (e.g., `Str`, `Para`, `Meta`, or
`Pandoc`). (That is why the two examples above are equivalent.)

For each filter, the document is traversed and each element
subjected to the filter. Elements for which the filter contains
an entry (i.e. a function of the same name) are passed to Lua
element filtering function. In other words, filter entries will
be called for each corresponding element in the document,
getting the respective element as input.

The return of a filter function must one of the following:

-   nil: this means that the object should remain unchanged.
-   a pandoc object: this must be of the same type as the input
    and will replace the original object.
-   a list of pandoc objects: these will replace the original
    object; the list is merged with the neighbors of the
    original objects (spliced into the list the original object
    belongs to); returning an empty list deletes the object.

The function's output must result in an element of the same type
as the input. This means a filter function acting on an inline
element must return either nil, an inline, or a list of inlines,
and a function filtering a block element must return one of nil,
a block, or a list of block elements. Pandoc will throw an error
if this condition is violated.

If there is no function matching the element's node type, then
the filtering system will look for a more general fallback
function. Two fallback functions are supported, `Inline` and
`Block`. Each matches elements of the respective type.

Elements without matching functions are left untouched.

See [module documentation](#module-pandoc) for a list of pandoc
elements.

## Filters on element sequences

For some filtering tasks, the it is necessary to know the order
in which elements occur in the document. It is not enough then to
inspect a single element at a time.

There are two special function names, which can be used to define
filters on lists of blocks or lists of inlines.

[`Inlines (inlines)`]{#inlines-filter}
:   If present in a filter, this function will be called on all
    lists of inline elements, like the content of a [Para]
    (paragraph) block, or the description of an [Image]. The
    `inlines` argument passed to the function will be a [List] of
    [Inlines] for each call.

[`Blocks (blocks)`]{#blocks-filter}
:   If present in a filter, this function will be called on all
    lists of block elements, like the content of a [MetaBlocks]
    meta element block, on each item of a list, and the main
    content of the [Pandoc] document. The `blocks` argument
    passed to the function will be a [List] of [Blocks] for each
    call.

These filter functions are special in that the result must either
be nil, in which case the list is left unchanged, or must be a
list of the correct type, i.e., the same type as the input
argument. Single elements are **not** allowed as return values,
as a single element in this context usually hints at a bug.

See ["Remove spaces before normal citations"][Inlines filter
example] for an example.

This functionality has been added in pandoc 2.9.2.

[Inlines filter example]: #remove-spaces-before-citations

## Execution Order

Element filter functions within a filter set are called in a
fixed order, skipping any which are not present:

  1. functions for [*Inline* elements](#type-inline),
  2. the [`Inlines`](#inlines-filter) filter function,
  2. functions for [*Block* elements](#type-block) ,
  2. the [`Blocks`](#inlines-filter) filter function,
  3. the [`Meta`](#type-meta) filter function, and last
  4. the [`Pandoc`](#type-pandoc) filter function.

It is still possible to force a different order by explicitly
returning multiple filter sets. For example, if the filter for
*Meta* is to be run before that for *Str*, one can write

``` lua
-- ... filter definitions ...

return {
  { Meta = Meta },  -- (1)
  { Str = Str }     -- (2)
}
```

Filter sets are applied in the order in which they are returned.
All functions in set (1) are thus run before those in (2),
causing the filter function for *Meta* to be run before the
filtering of *Str* elements is started.

## Global variables

Pandoc passes additional data to Lua filters by setting global
variables.

`FORMAT`
:   The global `FORMAT` is set to the format of the pandoc
    writer being used (`html5`, `latex`, etc.), so the behavior
    of a filter can be made conditional on the eventual output
    format.

`PANDOC_READER_OPTIONS`
:   Table of the options which were provided to the parser.

`PANDOC_VERSION`
:   Contains the pandoc version as a [Version] object which
    behaves like a numerically indexed table, most significant
    number first. E.g., for pandoc 2.7.3, the value of the
    variable is equivalent to a table `{2, 7, 3}`. Use
    `tostring(PANDOC_VERSION)` to produce a version string. This
    variable is also set in custom writers.

`PANDOC_API_VERSION`
:   Contains the version of the pandoc-types API against which
    pandoc was compiled. It is given as a numerically indexed
    table, most significant number first. E.g., if pandoc was
    compiled against pandoc-types 1.17.3, then the value of the
    variable will behave like the table `{1, 17, 3}`. Use
    `tostring(PANDOC_API_VERSION)` to produce a version string.
    This variable is also set in custom writers.

`PANDOC_SCRIPT_FILE`
:   The name used to involve the filter. This value can be used
    to find files relative to the script file. This variable is
    also set in custom writers.

`PANDOC_STATE`
:   The state shared by all readers and writers. It is used by
    pandoc to collect and pass information. The value of this
    variable is of type [CommonState] and
    is read-only.

# Pandoc Module

The `pandoc` Lua module is loaded into the filter's Lua
environment and provides a set of functions and constants to
make creation and manipulation of elements easier. The global
variable `pandoc` is bound to the module and should generally
not be overwritten for this reason.

Two major functionalities are provided by the module: element
creator functions and access to some of pandoc's main
functionalities.

## Element creation

Element creator functions like `Str`, `Para`, and `Pandoc` are
designed to allow easy creation of new elements that are simple
to use and can be read back from the Lua environment.
Internally, pandoc uses these functions to create the Lua
objects which are passed to element filter functions. This means
that elements created via this module will behave exactly as
those elements accessible through the filter function parameter.

## Exposed pandoc functionality

Some pandoc functions have been made available in Lua:

-   [`walk_block`](#pandoc.walk_block) and
    [`walk_inline`](#pandoc.walk_inline) allow filters to be applied
    inside specific block or inline elements;
-   [`read`](#pandoc.read) allows filters to parse strings into pandoc
    documents;
-   [`pipe`](#pandoc.pipe) runs an external command with input from and
    output to strings;
-   the [`pandoc.mediabag`](#module-pandoc.mediabag) module
    allows access to the "mediabag," which stores binary content
    such as images that may be included in the final document;
-   the [`pandoc.utils`](#module-pandoc.utils) module contains
    various utility functions.

# Lua interpreter initialization

Initialization of pandoc's Lua interpreter can be controlled by
placing a file `init.lua` in pandoc's data directory. A common
use-case would be to load additional modules, or even to alter
default modules.

The following snippet is an example of code that might be useful
when added to `init.lua`. The snippet adds all unicode-aware
functions defined in the [`text` module](#module-text) to the
default `string` module, prefixed with the string `uc_`.

``` lua
for name, fn in pairs(require 'text') do
  string['uc_' .. name] = fn
end
```

This makes it possible to apply these functions on strings using
colon syntax (`mystring:uc_upper()`).

# Examples

The following filters are presented as examples. A repository of
useful Lua filters (which may also serve as good examples) is
available at <https://github.com/pandoc/lua-filters>.

## Macro substitution

The following filter converts the string `{{helloworld}}` into
emphasized text "Hello, World".

``` lua
return {
  {
    Str = function (elem)
      if elem.text == "{{helloworld}}" then
        return pandoc.Emph {pandoc.Str "Hello, World"}
      else
        return elem
      end
    end,
  }
}
```

## Center images in LaTeX and HTML output

For LaTeX, wrap an image in LaTeX snippets which cause the image
to be centered horizontally. In HTML, the image element's style
attribute is used to achieve centering.

``` lua
-- Filter images with this function if the target format is LaTeX.
if FORMAT:match 'latex' then
  function Image (elem)
    -- Surround all images with image-centering raw LaTeX.
    return {
      pandoc.RawInline('latex', '\\hfill\\break{\\centering'),
      elem,
      pandoc.RawInline('latex', '\\par}')
    }
  end
end

-- Filter images with this function if the target format is HTML
if FORMAT:match 'html' then
  function Image (elem)
    -- Use CSS style to center image
    elem.attributes.style = 'margin:auto; display: block;'
    return elem
  end
end
```

## Setting the date in the metadata

This filter sets the date in the document's metadata to the
current date:

``` lua
function Meta(m)
  m.date = os.date("%B %e, %Y")
  return m
end
```

## Extracting information about links

This filter prints a table of all the URLs linked to in the
document, together with the number of links to that URL.

``` lua
links = {}

function Link (el)
  if links[el.target] then
    links[el.target] = links[el.target] + 1
  else
    links[el.target] = 1
  end
  return el
end

function Doc (blocks, meta)
  function strCell(str)
    return {pandoc.Plain{pandoc.Str(str)}}
  end
  local caption = {pandoc.Str "Link", pandoc.Space(), pandoc.Str "count"}
  local aligns = {pandoc.AlignDefault, pandoc.AlignLeft}
  local widths = {0.8, 0.2}
  local headers = {strCell "Target", strCell "Count"}
  local rows = {}
  for link, count in pairs(links) do
    rows[#rows + 1] = {strCell(link), strCell(count)}
  end
  return pandoc.Doc(
    {pandoc.Table(caption, aligns, widths, headers, rows)},
    meta
  )
end
```

## Remove spaces before citations

This filter removes all spaces preceding an "author-in-text"
citation. In Markdown, author-in-text citations (e.g.,
`@citekey`), must be preceded by a space. If these spaces are
undesired, they must be removed with a filter.

``` lua
local function is_space_before_author_in_text(spc, cite)
  return spc and spc.t == 'Space'
    and cite and cite.t == 'Cite'
    -- there must be only a single citation, and it must have
    -- mode 'AuthorInText'
    and #cite.citations == 1
    and cite.citations[1].mode == 'AuthorInText'
end

function Inlines (inlines)
  -- Go from end to start to avoid problems with shifting indices.
  for i = #inlines-1, 1, -1 do
    if is_space_before_author_in_text(inlines[i], inlines[i+1]) then
      inlines:remove(i)
    end
  end
  return inlines
end
```

## Replacing placeholders with their metadata value

Lua filter functions are run in the order

> *Inlines → Blocks → Meta → Pandoc*.

Passing information from a higher level (e.g., metadata) to a
lower level (e.g., inlines) is still possible by using two
filters living in the same file:

``` lua
local vars = {}

function get_vars (meta)
  for k, v in pairs(meta) do
    if type(v) == 'table' and v.t == 'MetaInlines' then
      vars["%" .. k .. "%"] = {table.unpack(v)}
    end
  end
end

function replace (el)
  if vars[el.text] then
    return pandoc.Span(vars[el.text])
  else
    return el
  end
end

return {{Meta = get_vars}, {Str = replace}}
```

If the contents of file `occupations.md` is

``` markdown
---
name: Samuel Q. Smith
occupation: Professor of Phrenology
---

Name

:   %name%

Occupation

:   %occupation%
```

then running `pandoc --lua-filter=meta-vars.lua occupations.md`
will output:

``` html
<dl>
<dt>Name</dt>
<dd><p><span>Samuel Q. Smith</span></p>
</dd>
<dt>Occupation</dt>
<dd><p><span>Professor of Phrenology</span></p>
</dd>
</dl>
```

## Modifying pandoc's `MANUAL.txt` for man pages

This is the filter we use when converting `MANUAL.txt` to man
pages. It converts level-1 headers to uppercase (using
`walk_block` to transform inline elements inside headers),
removes footnotes, and replaces links with regular text.

``` lua
-- we use preloaded text to get a UTF-8 aware 'upper' function
local text = require('text')

function Header(el)
    if el.level == 1 then
      return pandoc.walk_block(el, {
        Str = function(el)
            return pandoc.Str(text.upper(el.text))
        end })
    end
end

function Link(el)
    return el.content
end

function Note(el)
    return {}
end
```

## Creating a handout from a paper

This filter extracts all the numbered examples, section headers,
block quotes, and figures from a document, in addition to any
divs with class `handout`. (Note that only blocks at the "outer
level" are included; this ignores blocks inside nested
constructs, like list items.)

``` lua
-- creates a handout from an article, using its headings,
-- blockquotes, numbered examples, figures, and any
-- Divs with class "handout"

function Pandoc(doc)
    local hblocks = {}
    for i,el in pairs(doc.blocks) do
        if (el.t == "Div" and el.classes[1] == "handout") or
           (el.t == "BlockQuote") or
           (el.t == "OrderedList" and el.style == "Example") or
           (el.t == "Para" and #el.c == 1 and el.c[1].t == "Image") or
           (el.t == "Header") then
           table.insert(hblocks, el)
        end
    end
    return pandoc.Pandoc(hblocks, doc.meta)
end
```

## Counting words in a document

This filter counts the words in the body of a document (omitting
metadata like titles and abstracts), including words in code. It
should be more accurate than `wc -w` run directly on a Markdown
document, since the latter will count markup characters, like
the `#` in front of an ATX header, or tags in HTML documents, as
words. To run it, `pandoc --lua-filter wordcount.lua myfile.md`.

``` lua
-- counts words in a document

words = 0

wordcount = {
  Str = function(el)
    -- we don't count a word if it's entirely punctuation:
    if el.text:match("%P") then
        words = words + 1
    end
  end,

  Code = function(el)
    _,n = el.text:gsub("%S+","")
    words = words + n
  end,

  CodeBlock = function(el)
    _,n = el.text:gsub("%S+","")
    words = words + n
  end
}

function Pandoc(el)
    -- skip metadata, just count body:
    pandoc.walk_block(pandoc.Div(el.blocks), wordcount)
    print(words .. " words in body")
    os.exit(0)
end
```

## Converting ABC code to music notation

This filter replaces code blocks with class `abc` with images
created by running their contents through `abcm2ps` and
ImageMagick's `convert`. (For more on ABC notation, see
<https://abcnotation.com>.)

Images are added to the mediabag. For output to binary formats,
pandoc will use images in the mediabag. For textual formats, use
`--extract-media` to specify a directory where the files in the
mediabag will be written, or (for HTML only) use
`--self-contained`.

``` lua
-- Pandoc filter to process code blocks with class "abc" containing
-- ABC notation into images.
--
-- * Assumes that abcm2ps and ImageMagick's convert are in the path.
-- * For textual output formats, use --extract-media=abc-images
-- * For HTML formats, you may alternatively use --self-contained

local filetypes = { html = {"png", "image/png"}
                  , latex = {"pdf", "application/pdf"}
                  }
local filetype = filetypes[FORMAT][1] or "png"
local mimetype = filetypes[FORMAT][2] or "image/png"

local function abc2eps(abc, filetype)
    local eps = pandoc.pipe("abcm2ps", {"-q", "-O", "-", "-"}, abc)
    local final = pandoc.pipe("convert", {"-", filetype .. ":-"}, eps)
    return final
end

function CodeBlock(block)
    if block.classes[1] == "abc" then
        local img = abc2eps(block.text, filetype)
        local fname = pandoc.sha1(img) .. "." .. filetype
        pandoc.mediabag.insert(fname, mimetype, img)
        return pandoc.Para{ pandoc.Image({pandoc.Str("abc tune")}, fname) }
    end
end
```

## Building images with Ti*k*Z

This filter converts raw LaTeX Ti*k*Z environments into images. It
works with both PDF and HTML output. The Ti*k*Z code is compiled
to an image using `pdflatex`, and the image is converted from
pdf to svg format using
[`pdf2svg`](https://github.com/dawbarton/pdf2svg), so both of
these must be in the system path. Converted images are cached in
the working directory and given filenames based on a hash of the
source, so that they need not be regenerated each time the
document is built. (A more sophisticated version of this might
put these in a special cache directory.)

``` lua
local system = require 'pandoc.system'

local tikz_doc_template = [[
\documentclass{standalone}
\usepackage{xcolor}
\usepackage{tikz}
\begin{document}
\nopagecolor
%s
\end{document}
]]

local function tikz2image(src, filetype, outfile)
  system.with_temporary_directory('tikz2image', function (tmpdir)
    system.with_working_directory(tmpdir, function()
      local f = io.open('tikz.tex', 'w')
      f:write(tikz_doc_template:format(src))
      f:close()
      os.execute('pdflatex tikz.tex')
      if filetype == 'pdf' then
        os.rename('tikz.pdf', outfile)
      else
        os.execute('pdf2svg tikz.pdf ' .. outfile)
      end
    end)
  end)
end

extension_for = {
  html = 'svg',
  html4 = 'svg',
  html5 = 'svg',
  latex = 'pdf',
  beamer = 'pdf' }

local function file_exists(name)
  local f = io.open(name, 'r')
  if f ~= nil then
    io.close(f)
    return true
  else
    return false
  end
end

local function starts_with(start, str)
  return str:sub(1, #start) == start
end


function RawBlock(el)
  if starts_with('\\begin{tikzpicture}', el.text) then
    local filetype = extension_for[FORMAT] or 'svg'
    local fname = system.get_working_directory() .. '/' ..
        pandoc.sha1(el.text) .. '.' .. filetype
    if not file_exists(fname) then
      tikz2image(el.text, filetype, fname)
    end
    return pandoc.Para({pandoc.Image({}, fname)})
  else
   return el
  end
end
```

Example of use:

    pandoc --lua-filter tikz.lua -s -o cycle.html <<EOF
    Here is a diagram of the cycle:

    \begin{tikzpicture}

    \def \n {5}
    \def \radius {3cm}
    \def \margin {8} % margin in angles, depends on the radius

    \foreach \s in {1,...,\n}
    {
      \node[draw, circle] at ({360/\n * (\s - 1)}:\radius) {$\s$};
      \draw[->, >=latex] ({360/\n * (\s - 1)+\margin}:\radius)
        arc ({360/\n * (\s - 1)+\margin}:{360/\n * (\s)-\margin}:\radius);
    }
    \end{tikzpicture}
    EOF

# Lua type reference

This section describes the types of objects available to Lua
filters. See the [pandoc module](#module-pandoc) for
functions to create these objects.

## Shared Properties

### `clone`

`clone ()`

All instances of the types listed here, with the exception of
read-only objects, can be cloned via the `clone()` method.

Usage:

    local emph = pandoc.Emph {pandoc.Str 'important'}
    local cloned_emph = emph:clone()  -- note the colon

## Pandoc {#type-pandoc}

Pandoc document

Values of this type can be created with the
[`pandoc.Pandoc`](#pandoc.pandoc) constructor. Object equality is
determined via [`pandoc.utils.equals`].

`blocks`
:   document content ([List] of [Blocks])

`meta`
:   document meta information ([Meta] object)

## Meta {#type-meta}

Meta information on a document; string-indexed collection of
[MetaValues].

Values of this type can be created with the
[`pandoc.Meta`](#pandoc.meta) constructor. Object equality is
determined via [`pandoc.utils.equals`].

## MetaValue {#type-metavalue}

Document meta information items.

Object equality is determined via [`pandoc.utils.equals`].

### MetaBlocks {#type-metablocks}

A list of blocks usable as meta value ([List] of [Blocks]).

Fields:

`tag`, `t`
:   the literal `MetaBlocks` (string)

### MetaBool {#type-metabool}

Alias for Lua boolean, i.e. the values `true` and `false`.

### MetaInlines {#type-metainlines}

List of inlines used in metadata ([List] of [Inlines])

Values of this type can be created with the
[`pandoc.MetaInlines`](#pandoc.metainlines) constructor.

Fields:

`tag`, `t`
:   the literal `MetaInlines` (string)

### MetaList {#type-metalist}

A list of other metadata values ([List] of [MetaValues]).

Values of this type can be created with the
[`pandoc.MetaList`](#pandoc.metalist) constructor.

Fields:

`tag`, `t`
:   the literal `MetaList` (string)

All methods available for [List]s can be used on this type as
well.

### MetaMap {#type-metamap}

A string-indexed map of meta-values. (table).

Values of this type can be created with the
[`pandoc.MetaMap`](#pandoc.metamap) constructor.

Fields:

`tag`, `t`
:   the literal `MetaMap` (string)

*Note*: The fields will be shadowed if the map contains a field
with the same name as those listed.

### MetaString {#type-metastring}

Plain Lua string value (string).

## Block {#type-block}

Object equality is determined via [`pandoc.utils.equals`].

### BlockQuote {#type-blockquote}

A block quote element.

Values of this type can be created with the
[`pandoc.BlockQuote`](#pandoc.blockquote) constructor.

Fields:

`content`:
:   block content ([List] of [Blocks])

`tag`, `t`
:   the literal `BlockQuote` (string)

### BulletList {#type-bulletlist}

A bullet list.

Values of this type can be created with the
[`pandoc.BulletList`](#pandoc.bulletlist) constructor.

Fields:

`content`
:   list items ([List] of [List] of [Blocks])

`tag`, `t`
:   the literal `BulletList` (string)

### CodeBlock {#type-codeblock}

Block of code.

Values of this type can be created with the
[`pandoc.CodeBlock`](#pandoc.codeblock) constructor.

Fields:

`text`
:   code string (string)

`attr`
:   element attributes ([Attr])

`identifier`
:   alias for `attr.identifier` (string)

`classes`
:   alias for `attr.classes` ([List] of strings)

`attributes`
:   alias for `attr.attributes` ([Attributes])

`tag`, `t`
:   the literal `CodeBlock` (string)

### DefinitionList {#type-definitionlist}

Definition list, containing terms and their explanation.

Values of this type can be created with the
[`pandoc.DefinitionList`](#pandoc.definitionlist) constructor.

Fields:

`content`
:   list of items

`tag`, `t`
:   the literal `DefinitionList` (string)

### Div {#type-div}

Generic block container with attributes.

Values of this type can be created with the
[`pandoc.Div`](#pandoc.div) constructor.

Fields:

`content`
:   block content ([List] of [Blocks])

`attr`
:   element attributes ([Attr])

`identifier`
:   alias for `attr.identifier` (string)

`classes`
:   alias for `attr.classes` ([List] of
    strings)

`attributes`
:   alias for `attr.attributes` ([Attributes])

`tag`, `t`
:   the literal `Div` (string)

### Header {#type-header}

Creates a header element.

Values of this type can be created with the
[`pandoc.Header`](#pandoc.header) constructor.

Fields:

`level`
:   header level (integer)

`content`
:   inline content ([List] of [Inlines])

`attr`
:   element attributes ([Attr])

`identifier`
:   alias for `attr.identifier` (string)

`classes`
:   alias for `attr.classes` ([List] of strings)

`attributes`
:   alias for `attr.attributes`
    ([Attributes])

`tag`, `t`
:   the literal `Header` (string)

### HorizontalRule {#type-horizontalrule}

A horizontal rule.

Values of this type can be created with the
[`pandoc.HorizontalRule`](#pandoc.horizontalrule) constructor.

Fields:

`tag`, `t`
:   the literal `HorizontalRule` (string)

### LineBlock {#type-lineblock}

A line block, i.e. a list of lines, each separated from the next
by a newline.

Values of this type can be created with the
[`pandoc.LineBlock`](#pandoc.lineblock) constructor.

Fields:

`content`
:   inline content

`tag`, `t`
:   the literal `LineBlock` (string)

### Null {#type-null}

A null element; this element never produces any output in the
target format.

Values of this type can be created with the
[`pandoc.Null`](#pandoc.null) constructor.

`tag`, `t`
:   the literal `Null` (string)

### OrderedList {#type-orderedlist}

An ordered list.

Values of this type can be created with the
[`pandoc.OrderedList`](#pandoc.orderedlist) constructor.

Fields:

`content`
:   list items ([List] of [List] of [Blocks])

`listAttributes`
:   list parameters ([ListAttributes])

`start`
:   alias for `listAttributes.start` (integer)

`style`
:   alias for `listAttributes.style` (string)

`delimiter`
:   alias for `listAttributes.delimiter` (string)

`tag`, `t`
:   the literal `OrderedList` (string)

### Para {#type-para}

A paragraph.

Values of this type can be created with the
[`pandoc.Para`](#pandoc.para) constructor.

Fields:

`content`
:   inline content ([List] of [Inlines])

`tag`, `t`
:   the literal `Para` (string)

### Plain {#type-plain}

Plain text, not a paragraph.

Values of this type can be created with the
[`pandoc.Plain`](#pandoc.plain) constructor.

Fields:

`content`
:   inline content ([List] of [Inlines])

`tag`, `t`
:   the literal `Plain` (string)

### RawBlock {#type-rawblock}

Raw content of a specified format.

Values of this type can be created with the
[`pandoc.RawBlock`](#pandoc.rawblock) constructor.

Fields:

`format`
:   format of content (string)

`text`
:   raw content (string)

`tag`, `t`
:   the literal `RawBlock` (string)

### Table {#type-table}

A table.

Values of this type can be created with the
[`pandoc.Table`](#pandoc.table) constructor.

Fields:

`caption`
:   table caption ([List] of [Inlines])

`aligns`
:   column alignments ([List] of [Alignment]s)

`widths`
:   column widths (number)

`headers`
:   header row ([List] of [table cells](#type-table-cell))

`rows`
:   table rows ([List] of [List]s of [table
    cells](#type-table-cell))

`tag`, `t`
:   the literal `Table` (string)

A [table cell]{#type-table-cell} is a list of blocks.

*[Alignment]{#type-alignment}* is a string value indicating the
horizontal alignment of a table column. `AlignLeft`,
`AlignRight`, and `AlignCenter` leads cell content tob be
left-aligned, right-aligned, and centered, respectively. The
default alignment is `AlignDefault` (often equivalent to
centered).

## Inline {#type-inline}

Object equality is determined via [`pandoc.utils.equals`].

### Cite {#type-cite}

Citation.

Values of this type can be created with the
[`pandoc.Cite`](#pandoc.cite) constructor.

Fields:

`content`
:   ([List] of [Inlines])

`citations`
:   citation entries ([List] of [Citations])

`tag`, `t`
:   the literal `Cite` (string)

### Code {#type-code}

Inline code

Values of this type can be created with the
[`pandoc.Code`](#pandoc.code) constructor.

Fields:

`text`
:   code string (string)

`attr`
:   attributes ([Attr])

`identifier`
:   alias for `attr.identifier` (string)

`classes`
:   alias for `attr.classes` ([List] of strings)

`attributes`
:   alias for `attr.attributes` ([Attributes])

`tag`, `t`
:   the literal `Code` (string)

### Emph {#type-emph}

Emphasized text

Values of this type can be created with the
[`pandoc.Emph`](#pandoc.emph) constructor.

Fields:

`content`
:   inline content ([List] of [Inlines])

`tag`, `t`
:   the literal `Emph` (string)

### Image {#type-image}

Image: alt text (list of inlines), target

Values of this type can be created with the
[`pandoc.Image`](#pandoc.image) constructor.

Fields:

`attr`
:   attributes ([Attr])

`caption`
:   text used to describe the image ([List] of [Inlines])

`src`
:   path to the image file (string)

`title`
:   brief image description

`identifier`
:   alias for `attr.identifier` (string)

`classes`
:   alias for `attr.classes` ([List] of strings)

`attributes`
:   alias for `attr.attributes` ([Attributes])

`tag`, `t`
:   the literal `Image` (string)

### LineBreak {#type-linebreak}

Hard line break

Values of this type can be created with the
[`pandoc.LineBreak`](#pandoc.linebreak) constructor.

Fields:

`tag`, `t`
:   the literal `LineBreak` (string)

### Link {#type-link}

Hyperlink: alt text (list of inlines), target

Values of this type can be created with the
[`pandoc.Link`](#pandoc.link) constructor.

Fields:

`attr`
:   attributes ([Attr])

`content`
:   text for this link ([List] of [Inlines])

`target`
:   the link target (string)

`identifier`
:   alias for `attr.identifier` (string)

`classes`
:   alias for `attr.classes` ([List] of strings)

`attributes`
:   alias for `attr.attributes` ([Attributes])

`tag`, `t`
:   the literal `Link` (string)

### Math {#type-math}

TeX math (literal)

Values of this type can be created with the
[`pandoc.Math`](#pandoc.math) constructor.

Fields:

`mathtype`
:   specifier determining whether the math content should be
    shown inline (`InlineMath`) or on a separate line
    (`DisplayMath`) (string)

`text`
:   math content (string)

`tag`, `t`
:   the literal `Math` (string)

### Note {#type-note}

Footnote or endnote

Values of this type can be created with the
[`pandoc.Note`](#pandoc.note) constructor.

Fields:

`content`
:   ([List] of [Blocks])

`tag`, `t`
:   the literal `Note` (string)

### Quoted {#type-quoted}

Quoted text

Values of this type can be created with the
[`pandoc.Quoted`](#pandoc.quoted) constructor.

Fields:

`quotetype`
:   type of quotes to be used; one of `SingleQuote` or
    `DoubleQuote` (string)

`content`
:   quoted text ([List] of [Inlines])

`tag`, `t`
:   the literal `Quoted` (string)

### RawInline {#type-rawinline}

Raw inline

Values of this type can be created with the
[`pandoc.RawInline`](#pandoc.rawinline) constructor.

Fields:

`format`
:   the format of the content (string)

`text`
:   raw content (string)

`tag`, `t`
:   the literal `RawInline` (string)

### SmallCaps {#type-smallcaps}

Small caps text

Values of this type can be created with the
[`pandoc.SmallCaps`](#pandoc.smallcaps) constructor.

Fields:

`content`
:   ([List] of [Inlines])

`tag`, `t`
:   the literal `SmallCaps` (string)

### SoftBreak {#type-softbreak}

Soft line break

Values of this type can be created with the
[`pandoc.SoftBreak`](#pandoc.softbreak) constructor.

Fields:

`tag`, `t`
:   the literal `SoftBreak` (string)

### Space {#type-space}

Inter-word space

Values of this type can be created with the
[`pandoc.Space`](#pandoc.space) constructor.

Fields:

`tag`, `t`
:   the literal `Space` (string)

### Span {#type-span}

Generic inline container with attributes

Values of this type can be created with the
[`pandoc.Span`](#pandoc.span) constructor.

Fields:

`attr`
:   attributes ([Attr])

`content`
:   wrapped content ([List] of [Inlines])

`identifier`
:   alias for `attr.identifier` (string)

`classes`
:   alias for `attr.classes` ([List] of strings)

`attributes`
:   alias for `attr.attributes` ([Attributes])

`tag`, `t`
:   the literal `Span` (string)

### Str {#type-str}

Text

Values of this type can be created with the
[`pandoc.Str`](#pandoc.str) constructor.

Fields:

`text`
:   content (string)

`tag`, `t`
:   the literal `Str` (string)

### Strikeout {#type-strikeout}

Strikeout text

Values of this type can be created with the
[`pandoc.Strikeout`](#pandoc.strikeout) constructor.

Fields:

`content`
:   inline content ([List] of [Inlines])

`tag`, `t`
:   the literal `Strikeout` (string)

### Strong {#type-strong}

Strongly emphasized text

Values of this type can be created with the
[`pandoc.Strong`](#pandoc.strong) constructor.

Fields:

`content`
:   inline content ([List] of [Inlines])

`tag`, `t`
:   the literal `Strong` (string)

### Subscript {#type-subscript}

Subscripted text

Values of this type can be created with the
[`pandoc.Subscript`](#pandoc.subscript) constructor.

Fields:

`content`
:   inline content ([List] of [Inlines])

`tag`, `t`
:   the literal `Subscript` (string)

### Superscript {#type-superscript}

Superscripted text

Values of this type can be created with the
[`pandoc.Superscript`](#pandoc.superscript) constructor.

Fields:

`content`
:   inline content ([List] of [Inlines])

`tag`, `t`
:   the literal `Superscript` (string)

## Element components

### Attr {#type-attr}

A set of element attributes. Values of this type can be created
with the [`pandoc.Attr`](#pandoc.attr) constructor. For
convenience, it is usually not necessary to construct the value
directly if it is part of an element, and it is sufficient to
pass an HTML-like table. E.g., to create a span with identifier
"text" and classes "a" and "b", on can write:

    local span = pandoc.Span('text', {id = 'text', class = 'a b'})

This also works when using the `attr` setter:

    local span = pandoc.Span 'text'
    span.attr = {id = 'text', class = 'a b', other_attribute = '1'}

Object equality is determined via [`pandoc.utils.equals`].

Fields:

`identifier`
:   element identifier (string)

`classes`
:   element classes ([List] of strings)

`attributes`
:   collection of key/value pairs ([Attributes])

### Attributes {#type-attributes}

List of key/value pairs. Values can be accessed by using keys as
indices to the list table.

### Citation {#type-citation}

Single citation entry

Values of this type can be created with the
[`pandoc.Citation`](#pandoc.citation) constructor.

Object equality is determined via [`pandoc.utils.equals`].

Fields:

`id`
:   citation identifier, e.g., a bibtex key (string)

`mode`
:   citation mode, one of `AuthorInText`, `SuppressAuthor`, or
    `NormalCitation` (string)

`prefix`
:   citation prefix ([List] of [Inlines])

`suffix`
:   citation suffix ([List] of [Inlines])

`note_num`
:   note number (integer)

`hash`
:   hash (integer)

### ListAttributes {#type-listattributes}

List attributes

Values of this type can be created with the
[`pandoc.ListAttributes`](#pandoc.listattributes) constructor.

Object equality is determined via [`pandoc.utils.equals`].

Fields:

`start`
:   number of the first list item (integer)

`style`
:   style used for list numbers; possible values are
    `DefaultStyle`, `Example`, `Decimal`, `LowerRoman`,
    `UpperRoman`, `LowerAlpha`, and `UpperAlpha` (string)

`delimiter`
:   delimiter of list numbers; one of `DefaultDelim`, `Period`,
    `OneParen`, and `TwoParens` (string)

## ReaderOptions {#type-readeroptions}

Pandoc reader options

Fields:

`abbreviations`
:   set of known abbreviations (set of strings)

`columns`
:   number of columns in terminal (integer)

`default_image_extension`
:   default extension for images (string)

`extensions`
:   string representation of the syntax extensions bit field
    (string)

`indented_code_classes`
:   default classes for indented code blocks (list of strings)

`standalone`
:   whether the input was a standalone document with header
    (boolean)

`strip_comments`
:   HTML comments are stripped instead of parsed as raw HTML
    (boolean)

`tab_stop`
:   width (i.e. equivalent number of spaces) of tab stops
    (integer)

`track_changes`
:   track changes setting for docx; one of `AcceptChanges`,
    `RejectChanges`, and `AllChanges` (string)

## CommonState {#type-commonstate}

The state used by pandoc to collect information and make it
available to readers and writers.

Fields:

`input_files`
:   List of input files from command line
    ([List] of strings)

`output_file`
:   Output file from command line (string or nil)

`log`
:   A list of log messages in reverse order ([List] of
    [LogMessage]s)

`request_headers`
:   Headers to add for HTTP requests; table with header names as
    keys and header contents as value (table)

`resource_path`
:   Path to search for resources like included images
    ([List] of strings)

`source_url`
:   Absolute URL or directory of first source file (string or
    nil)

`user_data_dir`
:   Directory to search for data files (string or nil)

`trace`
:   Whether tracing messages are issued (boolean)

`verbosity`
:   Verbosity level; one of `INFO`, `WARNING`, `ERROR` (string)

## List {#type-list}

A list is any Lua table with integer indices. Indices start at
one, so if `alist = {'value'}` then `alist[1] == 'value'`.

Lists, when part of an element, or when generated during
marshalling, are made instances of the `pandoc.List` type for
convenience. The `pandoc.List` type is defined in the
[*pandoc.List*](#module-pandoc.list) module. See there for
available methods.

Values of this type can be created with the
[`pandoc.List`](#pandoc.list) constructor, turning a normal Lua
table into a List.

## LogMessage {#type-logmessage}

A pandoc log message. Objects have no fields, but can be
converted to a string via `tostring`.

## Version {#type-version}

A version object. This represents a software version like
"2.7.3". The object behaves like a numerically indexed table,
i.e., if `version` represents the version `2.7.3`, then

    version[1] == 2
    version[2] == 7
    version[3] == 3
    #version == 3   -- length

Comparisons are performed element-wise, i.e.

    Version '1.12' > Version '1.9'

Values of this type can be created with the
[`pandoc.types.Version`](#pandoc.types.version) constructor.

### `must_be_at_least`

`must_be_at_least(actual, expected [, error_message])`

Raise an error message if the actual version is older than the
expected version; does nothing if actual is equal to or newer
than the expected version.

Parameters:

`actual`
:   actual version specifier ([Version])

`expected`
:   minimum expected version ([Version])

`error_message`
:   optional error message template. The string is used as
    format string, with the expected and actual versions as
    arguments. Defaults to
    `"expected version %s or newer, got %s"`.

Usage:

    PANDOC_VERSION:must_be_at_least '2.7.3'
    PANDOC_API_VERSION:must_be_at_least(
      '1.17.4',
      'pandoc-types is too old: expected version %s, got %s'
    )

[Alignment]: #type-alignment
[Attr]: #type-attr
[Attributes]: #type-attributes
[Block]: #type-block
[Blocks]: #type-block
[Citation]: #type-citation
[Citations]: #type-citation
[CommonState]: #type-commonstate
[Image]: #type-image
[Inline]: #type-inline
[Inlines]: #type-inline
[List]: #type-list
[ListAttributes]: #type-listattributes
[Meta]: #type-meta
[MetaBlocks]: #type-metablocks
[MetaValue]: #type-metavalue
[MetaValues]: #type-metavalue
[LogMessage]: #type-logmessage
[Pandoc]: #type-pandoc
[Para]: #type-para
[Version]: #type-version
[`pandoc.utils.equals`]: #pandoc.utils.equals

# Module text

UTF-8 aware text manipulation functions, implemented in Haskell.
The module is made available as part of the `pandoc` module via
`pandoc.text`. The text module can also be loaded explicitly:

``` lua
-- uppercase all regular text in a document:
text = require 'text'
function Str (s)
  s.text = text.upper(s.text)
  return s
end
```

### lower {#text.lower}

`lower (s)`

Returns a copy of a UTF-8 string, converted to lowercase.

### upper {#text.upper}

`upper (s)`

Returns a copy of a UTF-8 string, converted to uppercase.

### reverse {#text.reverse}

`reverse (s)`

Returns a copy of a UTF-8 string, with characters reversed.

### len {#text.len}

`len (s)`

Returns the length of a UTF-8 string.

### sub {#text.sub}

`sub (s)`

Returns a substring of a UTF-8 string, using Lua's string
indexing rules.

# Module pandoc

Lua functions for pandoc scripts; includes constructors for
document tree elements, functions to parse text in a given
format, and functions to filter and modify a subtree.

## Pandoc

[`Pandoc (blocks[, meta])`]{#pandoc.pandoc}

:   A complete pandoc document

    Parameters:

    `blocks`:
    :   document content

    `meta`:
    :   document meta data

    Returns: [Pandoc] object

## Meta

[`Meta (table)`]{#pandoc.meta}

:   Create a new Meta object.

    Parameters:

    `table`:
    :   table containing document meta information

    Returns: [Meta] object

## MetaValue

[`MetaBlocks (blocks)`]{#pandoc.metablocks}

:   Meta blocks

    Parameters:

    `blocks`:
    :   blocks

    Returns: [MetaBlocks] object

[`MetaInlines (inlines)`]{#pandoc.metainlines}

:   Meta inlines

    Parameters:

    `inlines`:
    :   inlines

    Returns: [MetaInlines] object

[`MetaList (meta_values)`]{#pandoc.metalist}

:   Meta list

    Parameters:

    `meta_values`:
    :   list of meta values

    Returns: [MetaList] object

[`MetaMap (key_value_map)`]{#pandoc.metamap}

:   Meta map

    Parameters:

    `key_value_map`:
    :   a string-indexed map of meta values

    Returns: [MetaMap] object

[`MetaString (str)`]{#pandoc.metastring}

:   Creates string to be used in meta data.

    Parameters:

    `str`:
    :   string value

    Returns: [MetaString] object

[`MetaBool (bool)`]{#pandoc.metabool}

:   Creates boolean to be used in meta data.

    Parameters:

    `bool`:
    :   boolean value

    Returns: [MetaBool] object

## Blocks

[`BlockQuote (content)`]{#pandoc.blockquote}

:   Creates a block quote element

    Parameters:

    `content`:
    :   block content

    Returns: [BlockQuote] object

[`BulletList (items)`]{#pandoc.bulletlist}

:   Creates a bullet list.

    Parameters:

    `items`:
    :   list items

    Returns: [BulletList] object

[`CodeBlock (text[, attr])`]{#pandoc.codeblock}

:   Creates a code block element

    Parameters:

    `text`:
    :   code string

    `attr`:
    :   element attributes

    Returns: [CodeBlock] object

[`DefinitionList (content)`]{#pandoc.definitionlist}

:   Creates a definition list, containing terms and their
    explanation.

    Parameters:

    `content`:
    :   list of items

    Returns: [DefinitionList] object

[`Div (content[, attr])`]{#pandoc.div}

:   Creates a div element

    Parameters:

    `content`:
    :   block content

    `attr`:
    :   element attributes

    Returns: [Div] object

[`Header (level, content[, attr])`]{#pandoc.header}

:   Creates a header element.

    Parameters:

    `level`:
    :   header level

    `content`:
    :   inline content

    `attr`:
    :   element attributes

    Returns: [Header] object

[`HorizontalRule ()`]{#pandoc.horizontalrule}

:   Creates a horizontal rule.

    Returns: [HorizontalRule] object

[`LineBlock (content)`]{#pandoc.lineblock}

:   Creates a line block element.

    Parameters:

    `content`:
    :   inline content

    Returns: [LineBlock] object

[`Null ()`]{#pandoc.null}

:   Creates a null element.

    Returns: [Null] object

[`OrderedList (items[, listAttributes])`]{#pandoc.orderedlist}

:   Creates an ordered list.

    Parameters:

    `items`:
    :   list items

    `listAttributes`:
    :   list parameters

    Returns: [OrderedList](#type-orderedlist) object

[`Para (content)`]{#pandoc.para}

:   Creates a para element.

    Parameters:

    `content`:
    :   inline content

    Returns: [Para](#type-para) object

[`Plain (content)`]{#pandoc.plain}

:   Creates a plain element.

    Parameters:

    `content`:
    :   inline content

    Returns: [Plain](#type-plain) object

[`RawBlock (format, text)`]{#pandoc.rawblock}

:   Creates a raw content block of the specified format.

    Parameters:

    `format`:
    :   format of content

    `text`:
    :   string content

    Returns: [RawBlock](#type-rawblock) object

[`Table (caption, aligns, widths, headers, rows)`]{#pandoc.table}

:   Creates a table element.

    Parameters:

    `caption`:
    :   table caption

    `aligns`:
    :   alignments

    `widths`:
    :   column widths

    `headers`:
    :   header row

    `rows`:
    :   table rows

    Returns: [Table](#type-table) object

## Inline

[`Cite (content, citations)`]{#pandoc.cite}

:   Creates a Cite inline element

    Parameters:

    `content`:
    :   List of inlines

    `citations`:
    :   List of citations

    Returns: [Cite](#type-cite) object

[`Code (text[, attr])`]{#pandoc.code}

:   Creates a Code inline element

    Parameters:

    `text`:
    :   code string

    `attr`:
    :   additional attributes

    Returns: [Code](#type-code) object

[`Emph (content)`]{#pandoc.emph}

:   Creates an inline element representing emphasised text.

    Parameters:

    `content`:
    :   inline content

    Returns: [Emph](#type-emph) object

[`Image (caption, src[, title[, attr]])`]{#pandoc.image}

:   Creates a Image inline element

    Parameters:

    `caption`:
    :   text used to describe the image

    `src`:
    :   path to the image file

    `title`:
    :   brief image description

    `attr`:
    :   additional attributes

    Returns: [Image](#type-image) object

[`LineBreak ()`]{#pandoc.linebreak}

:   Create a LineBreak inline element

    Returns: [LineBreak](#type-linebreak) object

[`Link (content, target[, title[, attr]])`]{#pandoc.link}

:   Creates a link inline element, usually a hyperlink.

    Parameters:

    `content`:
    :   text for this link

    `target`:
    :   the link target

    `title`:
    :   brief link description

    `attr`:
    :   additional attributes

    Returns: [Link](#type-link) object

[`Math (mathtype, text)`]{#pandoc.math}

:   Creates a Math element, either inline or displayed.

    Parameters:

    `mathtype`:
    :   rendering specifier

    `text`:
    :   Math content

    Returns: [Math](#type-math) object

[`DisplayMath (text)`]{#pandoc.displaymath}

:   Creates a math element of type "DisplayMath" (DEPRECATED).

    Parameters:

    `text`:
    :   Math content

    Returns: [Math](#type-math) object

[`InlineMath (text)`]{#pandoc.inlinemath}

:   Creates a math element of type "InlineMath" (DEPRECATED).

    Parameters:

    `text`:
    :   Math content

    Returns: [Math](#type-math) object

[`Note (content)`]{#pandoc.note}

:   Creates a Note inline element

    Parameters:

    `content`:
    :   footnote block content

    Returns: [Note](#type-note) object

[`Quoted (quotetype, content)`]{#pandoc.quoted}

:   Creates a Quoted inline element given the quote type and
    quoted content.

    Parameters:

    `quotetype`:
    :   type of quotes to be used

    `content`:
    :   inline content

    Returns: [Quoted](#type-quoted) object

[`SingleQuoted (content)`]{#pandoc.singlequoted}

:   Creates a single-quoted inline element (DEPRECATED).

    Parameters:

    `content`:
    :   inline content

    Returns: [Quoted](#type-quoted)

[`DoubleQuoted (content)`]{#pandoc.doublequoted}

:   Creates a single-quoted inline element (DEPRECATED).

    Parameters:

    `content`:
    :   inline content

    Returns: [Quoted](#type-quoted)

[`RawInline (format, text)`]{#pandoc.rawinline}

:   Creates a raw inline element

    Parameters:

    `format`:
    :   format of the contents

    `text`:
    :   string content

    Returns: [RawInline](#type-rawinline) object

[`SmallCaps (content)`]{#pandoc.smallcaps}

:   Creates text rendered in small caps

    Parameters:

    `content`:
    :   inline content

    Returns: [SmallCaps](#type-smallcaps) object

[`SoftBreak ()`]{#pandoc.softbreak}

:   Creates a SoftBreak inline element.

    Returns: [SoftBreak](#type-softbreak) object

[`Space ()`]{#pandoc.space}

:   Create a Space inline element

    Returns: [Space](#type-space) object

[`Span (content[, attr])`]{#pandoc.span}

:   Creates a Span inline element

    Parameters:

    `content`:
    :   inline content

    `attr`:
    :   additional attributes

    Returns: [Span](#type-span) object

[`Str (text)`]{#pandoc.str}

:   Creates a Str inline element

    Parameters:

    `text`:
    :   content

    Returns: [Str](#type-str) object

[`Strikeout (content)`]{#pandoc.strikeout}

:   Creates text which is striked out.

    Parameters:

    `content`:
    :   inline content

    Returns: [Strikeout](#type-strikeout) object

[`Strong (content)`]{#pandoc.strong}

:   Creates a Strong element, whose text is usually displayed in
    a bold font.

    Parameters:

    `content`:
    :   inline content

    Returns: [Strong](#type-strong) object

[`Subscript (content)`]{#pandoc.subscript}

:   Creates a Subscript inline element

    Parameters:

    `content`:
    :   inline content

    Returns: [Subscript](#type-subscript) object

[`Superscript (content)`]{#pandoc.superscript}

:   Creates a Superscript inline element

    Parameters:

    `content`:
    :   inline content

    Returns: [Superscript](#type-superscript) object

## Element components

[`Attr ([identifier[, classes[, attributes]]])`]{#pandoc.attr}

:   Create a new set of attributes (Attr).

    Parameters:

    `identifier`:
    :   element identifier

    `classes`:
    :   element classes

    `attributes`:
    :   table containing string keys and values

    Returns: [Attr](#type-attr) object

[`Citation (id, mode[, prefix[, suffix[, note_num[, hash]]]])`]{#pandoc.citation}

:   Creates a single citation.

    Parameters:

    `id`:
    :   citation identifier (like a bibtex key)

    `mode`:
    :   citation mode

    `prefix`:
    :   citation prefix

    `suffix`:
    :   citation suffix

    `note_num`:
    :   note number

    `hash`:
    :   hash number

    Returns: [Citation](#type-citation) object

[`ListAttributes ([start[, style[, delimiter]]])`]{#pandoc.listattributes}

:   Creates a set of list attributes.

    Parameters:

    `start`:
    :   number of the first list item

    `style`:
    :   style used for list numbering

    `delimiter`:
    :   delimiter of list numbers

    Returns: [ListAttributes](#type-listattributes) object

## Constants

[`AuthorInText`]{#pandoc.authorintext}

:   Author name is mentioned in the text.

    See also: [Citation](#type-citation)

[`SuppressAuthor`]{#pandoc.suppressauthor}

:   Author name is suppressed.

    See also: [Citation](#type-citation)

[`NormalCitation`]{#pandoc.normalcitation}

:   Default citation style is used.

    See also: [Citation](#type-citation)

[`AlignLeft`]{#pandoc.alignleft}

:   Table cells aligned left.

    See also: [Table](#type-alignment)

[`AlignRight`]{#pandoc.alignright}

:   Table cells right-aligned.

    See also: [Table](#type-alignment)

[`AlignCenter`]{#pandoc.aligncenter}

:   Table cell content is centered.

    See also: [Table](#type-alignment)

[`AlignDefault`]{#pandoc.aligndefault}

:   Table cells are alignment is unaltered.

    See also: [Table](#type-alignment)

[`DefaultDelim`]{#pandoc.defaultdelim}

:   Default list number delimiters are used.

    See also: [ListAttributes](#type-listattributes)

[`Period`]{#pandoc.period}

:   List numbers are delimited by a period.

    See also: [ListAttributes](#type-listattributes)

[`OneParen`]{#pandoc.oneparen}

:   List numbers are delimited by a single parenthesis.

    See also: [ListAttributes](#type-listattributes)

[`TwoParens`]{#pandoc.twoparens}

:   List numbers are delimited by a double parentheses.

    See also: [ListAttributes](#type-listattributes)

[`DefaultStyle`]{#pandoc.defaultstyle}

:   List are numbered in the default style

    See also: [ListAttributes](#type-listattributes)

[`Example`]{#pandoc.example}

:   List items are numbered as examples.

    See also: [ListAttributes](#type-listattributes)

[`Decimal`]{#pandoc.decimal}

:   List are numbered using decimal integers.

    See also: [ListAttributes](#type-listattributes)

[`LowerRoman`]{#pandoc.lowerroman}

:   List are numbered using lower-case roman numerals.

    See also: [ListAttributes](#type-listattributes)

[`UpperRoman`]{#pandoc.upperroman}

:   List are numbered using upper-case roman numerals

    See also: [ListAttributes](#type-listattributes)

[`LowerAlpha`]{#pandoc.loweralpha}

:   List are numbered using lower-case alphabetic characters.

    See also: [ListAttributes](#type-listattributes)

[`UpperAlpha`]{#pandoc.upperalpha}

:   List are numbered using upper-case alphabetic characters.

    See also: [ListAttributes](#type-listattributes)

[`sha1`]{#pandoc.sha1}

:   Alias for [`pandoc.utils.sha1`](#pandoc.utils.sha1)
    (DEPRECATED).

## Helper functions

### pipe {#pandoc.pipe}

`pipe (command, args, input)`

Runs command with arguments, passing it some input, and returns
the output.

Returns:

-   Output of command.

Raises:

-   A table containing the keys `command`, `error_code`, and
    `output` is thrown if the command exits with a non-zero
    error code.

Usage:

    local output = pandoc.pipe("sed", {"-e","s/a/b/"}, "abc")

### walk\_block {#pandoc.walk_block}

`walk_block (element, filter)`

Apply a filter inside a block element, walking its contents.

Parameters:

`element`:
:   the block element

`filter`:
:   a Lua filter (table of functions) to be applied within the
    block element

Returns: the transformed block element

### walk\_inline {#pandoc.walk_inline}

`walk_inline (element, filter)`

Apply a filter inside an inline element, walking its contents.

Parameters:

`element`:
:   the inline element

`filter`:
:   a Lua filter (table of functions) to be applied within the
    inline element

Returns: the transformed inline element

### read {#pandoc.read}

`read (markup[, format])`

Parse the given string into a Pandoc document.

Parameters:

`markup`:
:   the markup to be parsed

`format`:
:   format specification, defaults to `"markdown"`.

Returns: pandoc document

Usage:

    local org_markup = "/emphasis/"  -- Input to be read
    local document = pandoc.read(org_markup, "org")
    -- Get the first block of the document
    local block = document.blocks[1]
    -- The inline element in that block is an `Emph`
    assert(block.content[1].t == "Emph")

# Module pandoc.utils

This module exposes internal pandoc functions and utility
functions.

The module is loaded as part of the `pandoc` module and
available as `pandoc.utils`. In versions up-to and including
pandoc 2.6, this module had to be loaded explicitly. Example:

    pandoc.utils = require 'pandoc.utils'

Use the above for backwards compatibility.

### blocks\_to\_inlines {#pandoc.utils.blocks_to_inlines}

`blocks_to_inlines (blocks[, sep])`

Squash a list of blocks into a list of inlines.

Parameters:

`blocks`:
:   List of [Blocks](#type-block) to be flattened.

`sep`:
:   List of [Inlines](#type-inline) inserted as separator between
    two consecutive blocks; defaults to
    `{ pandoc.Space(), pandoc.Str'¶', pandoc.Space()}`.

Returns:

-   [List](#type-list) of [Inlines](#type-inline)

Usage:

    local blocks = {
      pandoc.Para{ pandoc.Str 'Paragraph1' },
      pandoc.Para{ pandoc.Emph 'Paragraph2' }
    }
    local inlines = pandoc.utils.blocks_to_inlines(blocks)
    -- inlines = {
    --   pandoc.Str 'Paragraph1',
    --   pandoc.Space(), pandoc.Str'¶', pandoc.Space(),
    --   pandoc.Emph{ pandoc.Str 'Paragraph2' }
    -- }

### equals {#pandoc.utils.equals}

`equals (element1, element2)`

Test equality of AST elements. Elements in Lua are considered
equal if and only if the objects obtained by unmarshaling are
equal.

Parameters:

`element1`, `element2`:
:   Objects to be compared. Acceptable input types are [Pandoc],
    [Meta], [MetaValue], [Block], [Inline], [Attr],
    [ListAttributes], and [Citation].

Returns:

-   Whether the two objects represent the same element (boolean)

### make\_sections {#pandoc.utils.make_sections}

`make_sections (number_sections, base_level, blocks)`

Converst list of [Blocks](#type-block) into sections.
`Div`s will be created beginning at each `Header`
and containing following content until the next `Header`
of comparable level.  If `number_sections` is true,
a `number` attribute will be added to each `Header`
containing the section number. If `base_level` is
non-null, `Header` levels will be reorganized so
that there are no gaps, and so that the base level
is the level specified.

Returns:

-   List of [Blocks](#type-block).

Usage:

    local blocks = {
      pandoc.Header(2, pandoc.Str 'first'),
      pandoc.Header(2, pandoc.Str 'second'),
    }
    local newblocks = pandoc.utils.make_sections(true, 1, blocks)

### run\_json\_filter {#pandoc.utils.run_json_filter}

`run_json_filter (doc, filter[, args])`

Filter the given doc by passing it through the a JSON filter.

Parameters:

`doc`:
:   the Pandoc document to filter

`filter`:
:   filter to run

`args`:
:   list of arguments passed to the filter. Defaults to
    `{FORMAT}`.

Returns:

-   ([Pandoc](#type-pandoc)) Filtered document

Usage:

    -- Assumes `some_blocks` contains blocks for which a
    -- separate literature section is required.
    local sub_doc = pandoc.Pandoc(some_blocks, metadata)
    sub_doc_with_bib = pandoc.utils.run_json_filter(
      sub_doc,
      'pandoc-citeproc'
    )
    some_blocks = sub_doc.blocks -- some blocks with bib

### normalize\_date {#pandoc.utils.normalize_date}

`normalize_date (date_string)`

Parse a date and convert (if possible) to "YYYY-MM-DD" format.
We limit years to the range 1601-9999 (ISO 8601 accepts greater
than or equal to 1583, but MS Word only accepts dates starting
1601).

Returns:

-   A date string, or nil when the conversion failed.

### sha1 {#pandoc.utils.sha1}

`sha1 (contents)`

Returns the SHA1 has of the contents.

Returns:

-   SHA1 hash of the contents.

Usage:

    local fp = pandoc.utils.sha1("foobar")

### stringify {#pandoc.utils.stringify}

`stringify (element)`

Converts the given element (Pandoc, Meta, Block, or Inline) into
a string with all formatting removed.

Returns:

-   A plain string representation of the given element.

Usage:

    local inline = pandoc.Emph{pandoc.Str 'Moin'}
    -- outputs "Moin"
    print(pandoc.utils.stringify(inline))

### to\_roman\_numeral {#pandoc.utils.to_roman_numeral}

`to_roman_numeral (integer)`

Converts an integer \< 4000 to uppercase roman numeral.

Returns:

-   A roman numeral string.

Usage:

    local to_roman_numeral = pandoc.utils.to_roman_numeral
    local pandoc_birth_year = to_roman_numeral(2006)
    -- pandoc_birth_year == 'MMVI'

# Module pandoc.mediabag

The `pandoc.mediabag` module allows accessing pandoc's media
storage. The "media bag" is used when pandoc is called with the
`--extract-media` or (for HTML only) `--self-contained` option.

The module is loaded as part of module `pandoc` and can either
be accessed via the `pandoc.mediabag` field, or explicitly
required, e.g.:

    local mb = require 'pandoc.mediabag'

### delete {#pandoc.mediabag.delete}

`delete (filepath)`

Removes a single entry from the media bag.

Parameters:

`filepath`:
:   filename of the item to be deleted. The media bag will be
    left unchanged if no entry with the given filename exists.

### empty {#pandoc.mediabag.empty}

`empty ()`

Clear-out the media bag, deleting all items.

### insert {#pandoc.mediabag.insert}

`insert (filepath, mime_type, contents)`

Adds a new entry to pandoc's media bag.

Parameters:

`filepath`:
:   filename and path relative to the output folder.

`mime_type`:
:   the file's MIME type

`contents`:
:   the binary contents of the file.

Usage:

    local fp = "media/hello.txt"
    local mt = "text/plain"
    local contents = "Hello, World!"
    pandoc.mediabag.insert(fp, mt, contents)

### items {#pandoc.mediabag.items}

`items ()`

Returns an iterator triple to be used with Lua's generic `for`
statement. The iterator returns the filepath, MIME type, and
content of a media bag item on each invocation. Items are
processed one-by-one to avoid excessive memory use.

This function should be used only when full access to all items,
including their contents, is required. For all other cases,
[`list`](#pandoc.mediabag.list) should be preferred.

Returns:

-   The iterator function; must be called with the iterator
    state and the current iterator value.
-   Iterator state -- an opaque value to be passed to the
    iterator function.
-   Initial iterator value.

Usage:

    for fp, mt, contents in pandoc.mediabag.items() do
      -- print(fp, mt, contents)
    end

### list {#pandoc.mediabag.list}

`list ()`

Get a summary of the current media bag contents.

Returns: A list of elements summarizing each entry in the media
bag. The summary item contains the keys `path`, `type`, and
`length`, giving the filepath, MIME type, and length of contents
in bytes, respectively.

Usage:

    -- calculate the size of the media bag.
    local mb_items = pandoc.mediabag.list()
    local sum = 0
    for i = 1, #mb_items do
        sum = sum + mb_items[i].length
    end
    print(sum)

### lookup {#pandoc.mediabag.lookup}

`lookup (filepath)`

Lookup a media item in the media bag, and return its MIME type
and contents.

Parameters:

`filepath`:
:   name of the file to look up.

Returns:

-   the entry's MIME type, or nil if the file was not found.
-   contents of the file, or nil if the file was not found.

Usage:

    local filename = "media/diagram.png"
    local mt, contents = pandoc.mediabag.lookup(filename)

### fetch {#pandoc.mediabag.fetch}

`fetch (source, base_url)`

Fetches the given source from a URL or local file. Returns two
values: the contents of the file and the MIME type (or an empty
string).

Returns:

-   the entries MIME type, or nil if the file was not found.
-   contents of the file, or nil if the file was not found.

Usage:

    local diagram_url = "https://pandoc.org/diagram.jpg"
    local mt, contents = pandoc.mediabag.fetch(diagram_url, ".")

# Module pandoc.List

The this module defines pandoc's list type. It comes with useful
methods and convenience functions.

## Constructor

[`pandoc.List([table])`]{#pandoc.list}

:   Create a new List. If the optional argument `table` is given,
    set the metatable of that value to `pandoc.List`. This is an
    alias for [`pandoc.List:new([table])`](#pandoc.list:new).

## Metamethods

[`pandoc.List:__concat (list)`]{#pandoc.list:__concat}

:   Concatenates two lists.

    Parameters:

    `list`:
    :   second list concatenated to the first

    Returns: a new list containing all elements from list1 and
    list2

## Methods

[`pandoc.List:clone ()`]{#pandoc.list:clone}

:   Returns a (shallow) copy of the list.

[`pandoc.List:extend (list)`]{#pandoc.list:extend}

:   Adds the given list to the end of this list.

    Parameters:

    `list`:
    :   list to appended

[`pandoc.List:find (needle, init)`]{#pandoc.list:find}

:   Returns the value and index of the first occurrence of the
    given item.

    Parameters:

    `needle`:
    :   item to search for

    `init`:
    :   index at which the search is started

    Returns: first item equal to the needle, or nil if no such
    item exists.

[`pandoc.List:find_if (pred, init)`]{#pandoc.list:find_if}

:   Returns the value and index of the first element for which
    the predicate holds true.

    Parameters:

    `pred`:
    :   the predicate function

    `init`:
    :   index at which the search is started

    Returns: first item for which \`test\` succeeds, or nil if
    no such item exists.

[`pandoc.List:filter (pred)`]{#pandoc.list:filter}

:   Returns a new list containing all items satisfying a given
    condition.

    Parameters:

    `pred`:
    :   condition items must satisfy.

    Returns: a new list containing all items for which \`test\`
    was true.

[`pandoc.List:includes (needle, init)`]{#pandoc.list:includes}

:   Checks if the list has an item equal to the given needle.

    Parameters:

    `needle`:
    :   item to search for

    `init`:
    :   index at which the search is started

    Returns: true if a list item is equal to the needle, false
    otherwise

[`pandoc.List:insert ([pos], value)`]{#pandoc.list:insert}

:   Inserts element `value` at position `pos` in list, shifting
    elements to the next-greater indix if necessary.

    This function is identical to
    [`table.insert`](https://www.lua.org/manual/5.3/manual.html#6.6).

    Parameters:

    `pos`:
    :   index of the new value; defaults to length of the list + 1

    `value`:
    :   value to insert into the list

[`pandoc.List:map (fn)`]{#pandoc.list:map}

:   Returns a copy of the current list by applying the given
    function to all elements.

    Parameters:

    `fn`:
    :   function which is applied to all list items.

[`pandoc.List:new([table])`]{#pandoc.list:new}

:   Create a new List. If the optional argument `table` is given,
    set the metatable of that value to `pandoc.List`.

    Parameters:

    `table`:
    :   table which should be treatable as a list; defaults to an
        empty table

    Returns: the updated input value

[`pandoc.List:remove ([pos])`]{#pandoc.list:remove}

:    Removes the element at position `pos`, returning the value
     of the removed element.

     This function is identical to
     [`table.remove`](https://www.lua.org/manual/5.3/manual.html#6.6).

    Parameters:

    `pos`:
    :   position of the list value that will be remove; defaults
        to the index of the last element

    Returns: the removed element

[`pandoc.List:sort ([comp])`]{#pandoc.list:sort}

:   Sorts list elements in a given order, in-place. If `comp` is
    given, then it must be a function that receives two list
    elements and returns true when the first element must come
    before the second in the final order (so that, after the
    sort, `i < j` implies `not comp(list[j],list[i]))`. If comp
    is not given, then the standard Lua operator `<` is used
    instead.

    Note that the comp function must define a strict partial
    order over the elements in the list; that is, it must be
    asymmetric and transitive. Otherwise, no valid sort may be
    possible.

    The sort algorithm is not stable: elements considered equal
    by the given order may have their relative positions changed
    by the sort.

    This function is identical to
    [`table.sort`](https://www.lua.org/manual/5.3/manual.html#6.6).

    Parameters:

    `comp`:
    :   Comparison function as described above.

# Module pandoc.system

Access to system information and functionality.

## Static Fields

### arch {#pandoc.system.arch}

The machine architecture on which the program is running.

### os {#pandoc.system.os}

The operating system on which the program is running.

## Functions

### environment {#pandoc.system.environment}

`environment ()`

Retrieve the entire environment as a string-indexed table.

Returns:

-   A table mapping environment variables names to their string
    value (table).

### get\_working\_directory {#pandoc.system.get_working_directory}

`get_working_directory ()`

Obtain the current working directory as an absolute path.

Returns:

-   The current working directory (string).

### with\_environment {#pandoc.system.with_environment}

`with_environment (environment, callback)`

Run an action within a custom environment. Only the environment
variables given by `environment` will be set, when `callback` is
called. The original environment is restored after this function
finishes, even if an error occurs while running the callback
action.

Parameters:

`environment`
:   Environment variables and their values to be set before
    running `callback`. (table with string keys and string
    values)

`callback`
:   Action to execute in the custom environment (function)

Returns:

-   The result(s) of the call to `callback`

### with\_temporary\_directory {#pandoc.system.with_temporary_directory}

`with_temporary_directory ([parent_dir,] templ, callback)`

Create and use a temporary directory inside the given directory.
The directory is deleted after the callback returns.

Parameters:

`parent_dir`
:   Parent directory to create the directory in (string). If
    this parameter is omitted, the system's canonical temporary
    directory is used.

`templ`
:   Directory name template (string).

`callback`
:   Function which takes the name of the temporary directory as
    its first argument (function).

Returns:

-   The result of the call to `callback`.

### with\_working\_directory {#pandoc.system.with_working_directory}

`with_working_directory (directory, callback)`

Run an action within a different directory. This function will
change the working directory to `directory`, execute `callback`,
then switch back to the original working directory, even if an
error occurs while running the callback action.

Parameters:

`directory`
:   Directory in which the given `callback` should be executed
    (string)

`callback`
:   Action to execute in the given directory (function)

Returns:

-   The result(s) of the call to `callback`

# Module pandoc.types

Constructors for types which are not part of the pandoc AST.

### Version {#pandoc.types.version}

`Version (version_specifier)`

Creates a Version object.

Parameters:

`version_specifier`:
:   Version specifier: this can be a version string like
    `'2.7.3'`, a list of integers like `{2, 7, 3}`, a single
    integer, or a [Version].

Returns:

-   A new [Version] object.