discontinued / server · Files

webappapis.html 104 KB
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 
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html lang="en-US-x-Hixie" ><head><title>6 Web application APIs &#8212; HTML5 </title><style type="text/css">
   pre { margin-left: 2em; white-space: pre-wrap; }
   h2 { margin: 3em 0 1em 0; }
   h3 { margin: 2.5em 0 1em 0; }
   h4 { margin: 2.5em 0 0.75em 0; }
   h5, h6 { margin: 2.5em 0 1em; }
   h1 + h2, h1 + h2 + h2 { margin: 0.75em 0 0.75em; }
   h2 + h3, h3 + h4, h4 + h5, h5 + h6 { margin-top: 0.5em; }
   p { margin: 1em 0; }
   hr:not(.top) { display: block; background: none; border: none; padding: 0; margin: 2em 0; height: auto; }
   dl, dd { margin-top: 0; margin-bottom: 0; }
   dt { margin-top: 0.75em; margin-bottom: 0.25em; clear: left; }
   dt + dt { margin-top: 0; }
   dd dt { margin-top: 0.25em; margin-bottom: 0; }
   dd p { margin-top: 0; }
   dd dl + p { margin-top: 1em; }
   dd table + p { margin-top: 1em; }
   p + * > li, dd li { margin: 1em 0; }
   dt, dfn { font-weight: bold; font-style: normal; }
   dt dfn { font-style: italic; }
   pre, code { font-size: inherit; font-family: monospace; font-variant: normal; }
   pre strong { color: black; font: inherit; font-weight: bold; background: yellow; }
   pre em { font-weight: bolder; font-style: normal; }
   @media screen { code { color: orangered; } code :link, code :visited { color: inherit; } }
   var sub { vertical-align: bottom; font-size: smaller; position: relative; top: 0.1em; }
   table { border-collapse: collapse; border-style: hidden hidden none hidden; }
   table thead, table tbody { border-bottom: solid; }
   table tbody th:first-child { border-left: solid; }
   table tbody th { text-align: left; }
   table td, table th { border-left: solid; border-right: solid; border-bottom: solid thin; vertical-align: top; padding: 0.2em; }
   blockquote { margin: 0 0 0 2em; border: 0; padding: 0; font-style: italic; }

   .bad, .bad *:not(.XXX) { color: gray; border-color: gray; background: transparent; }
   .matrix, .matrix td { border: none; text-align: right; }
   .matrix { margin-left: 2em; }
   .dice-example { border-collapse: collapse; border-style: hidden solid solid hidden; border-width: thin; margin-left: 3em; }
   .dice-example caption { width: 30em; font-size: smaller; font-style: italic; padding: 0.75em 0; text-align: left; }
   .dice-example td, .dice-example th { border: solid thin; width: 1.35em; height: 1.05em; text-align: center; padding: 0; }

   .toc dfn, h1 dfn, h2 dfn, h3 dfn, h4 dfn, h5 dfn, h6 dfn { font: inherit; }
   img.extra { float: right; }
   pre.idl { border: solid thin; background: #EEEEEE; color: black; padding: 0.5em 1em; }
   pre.idl :link, pre.idl :visited { color: inherit; background: transparent; }
   pre.css { border: solid thin; background: #FFFFEE; color: black; padding: 0.5em 1em; }
   pre.css:first-line { color: #AAAA50; }
   dl.domintro { color: green; margin: 2em 0 2em 2em; padding: 0.5em 1em; border: none; background: #DDFFDD; }
   hr + dl.domintro, div.impl + dl.domintro { margin-top: 2.5em; margin-bottom: 1.5em; }
   dl.domintro dt, dl.domintro dt * { color: black; text-decoration: none; }
   dl.domintro dd { margin: 0.5em 0 1em 2em; padding: 0; }
   dl.domintro dd p { margin: 0.5em 0; }
   dl.switch { padding-left: 2em; }
   dl.switch > dt { text-indent: -1.5em; }
   dl.switch > dt:before { content: '\21AA'; padding: 0 0.5em 0 0; display: inline-block; width: 1em; text-align: right; line-height: 0.5em; }
   dl.triple { padding: 0 0 0 1em; }
   dl.triple dt, dl.triple dd { margin: 0; display: inline }
   dl.triple dt:after { content: ':'; }
   dl.triple dd:after { content: '\A'; white-space: pre; }
   .diff-old { text-decoration: line-through; color: silver; background: transparent; }
   .diff-chg, .diff-new { text-decoration: underline; color: green; background: transparent; }
   a .diff-new { border-bottom: 1px blue solid; }

   h2 { page-break-before: always; }
   h1, h2, h3, h4, h5, h6 { page-break-after: avoid; }
   h1 + h2, hr + h2.no-toc { page-break-before: auto; }

   p  > span:not([title=""]):not([class="XXX"]):not([class="impl"]):not([class="note"]),
   li > span:not([title=""]):not([class="XXX"]):not([class="impl"]):not([class="note"]), { border-bottom: solid #9999CC; }

   div.head { margin: 0 0 1em; padding: 1em 0 0 0; }
   div.head p { margin: 0; }
   div.head h1 { margin: 0; }
   div.head .logo { float: right; margin: 0 1em; }
   div.head .logo img { border: none } /* remove border from top image */
   div.head dl { margin: 1em 0; }
   div.head p.copyright, div.head p.alt { font-size: x-small; font-style: oblique; margin: 0; }

   body > .toc > li { margin-top: 1em; margin-bottom: 1em; }
   body > .toc.brief > li { margin-top: 0.35em; margin-bottom: 0.35em; }
   body > .toc > li > * { margin-bottom: 0.5em; }
   body > .toc > li > * > li > * { margin-bottom: 0.25em; }
   .toc, .toc li { list-style: none; }

   .brief { margin-top: 1em; margin-bottom: 1em; line-height: 1.1; }
   .brief li { margin: 0; padding: 0; }
   .brief li p { margin: 0; padding: 0; }

   .category-list { margin-top: -0.75em; margin-bottom: 1em; line-height: 1.5; }
   .category-list::before { content: '\21D2\A0'; font-size: 1.2em; font-weight: 900; }
   .category-list li { display: inline; }
   .category-list li:not(:last-child)::after { content: ', '; }
   .category-list li > span, .category-list li > a { text-transform: lowercase; }
   .category-list li * { text-transform: none; } /* don't affect <code> nested in <a> */

   .XXX { color: #E50000; background: white; border: solid red; padding: 0.5em; margin: 1em 0; }
   .XXX > :first-child { margin-top: 0; }
   p .XXX { line-height: 3em; }
   .annotation { border: solid thin black; background: #0C479D; color: white; position: relative; margin: 8px 0 20px 0; }
   .annotation:before { position: absolute; left: 0; top: 0; width: 100%; height: 100%; margin: 6px -6px -6px 6px; background: #333333; z-index: -1; content: ''; }
   .annotation :link, .annotation :visited { color: inherit; }
   .annotation :link:hover, .annotation :visited:hover { background: transparent; }
   .annotation span { border: none ! important; }
   .note { color: green; background: transparent; font-family: sans-serif; }
   .warning { color: red; background: transparent; }
   .note, .warning { font-weight: bolder; font-style: italic; }
   p.note, div.note { padding: 0.5em 2em; }
   span.note { padding: 0 2em; }
   .note p:first-child, .warning p:first-child { margin-top: 0; }
   .note p:last-child, .warning p:last-child { margin-bottom: 0; }
   .warning:before { font-style: normal; }
   p.note:before { content: 'Note: '; }
   p.warning:before { content: '\26A0 Warning! '; }

   .bookkeeping:before { display: block; content: 'Bookkeeping details'; font-weight: bolder; font-style: italic; }
   .bookkeeping { font-size: 0.8em; margin: 2em 0; }
   .bookkeeping p { margin: 0.5em 2em; display: list-item; list-style: square; }
   .bookkeeping dt { margin: 0.5em 2em 0; }
   .bookkeeping dd { margin: 0 3em 0.5em; }

   h4 { position: relative; z-index: 3; }
   h4 + .element, h4 + div + .element { margin-top: -2.5em; padding-top: 2em; }
   .element {
     background: #EEEEFF;
     color: black;
     margin: 0 0 1em 0.15em;
     padding: 0 1em 0.25em 0.75em;
     border-left: solid #9999FF 0.25em;
     position: relative;
     z-index: 1;
   }
   .element:before {
     position: absolute;
     z-index: 2;
     top: 0;
     left: -1.15em;
     height: 2em;
     width: 0.9em;
     background: #EEEEFF;
     content: ' ';
     border-style: none none solid solid;
     border-color: #9999FF;
     border-width: 0.25em;
   }

   .example { display: block; color: #222222; background: #FCFCFC; border-left: double; margin-left: 2em; padding-left: 1em; }
   td > .example:only-child { margin: 0 0 0 0.1em; }

   ul.domTree, ul.domTree ul { padding: 0 0 0 1em; margin: 0; }
   ul.domTree li { padding: 0; margin: 0; list-style: none; position: relative; }
   ul.domTree li li { list-style: none; }
   ul.domTree li:first-child::before { position: absolute; top: 0; height: 0.6em; left: -0.75em; width: 0.5em; border-style: none none solid solid; content: ''; border-width: 0.1em; }
   ul.domTree li:not(:last-child)::after { position: absolute; top: 0; bottom: -0.6em; left: -0.75em; width: 0.5em; border-style: none none solid solid; content: ''; border-width: 0.1em; }
   ul.domTree span { font-style: italic; font-family: serif; }
   ul.domTree .t1 code { color: purple; font-weight: bold; }
   ul.domTree .t2 { font-style: normal; font-family: monospace; }
   ul.domTree .t2 .name { color: black; font-weight: bold; }
   ul.domTree .t2 .value { color: blue; font-weight: normal; }
   ul.domTree .t3 code, .domTree .t4 code, .domTree .t5 code { color: gray; }
   ul.domTree .t7 code, .domTree .t8 code { color: green; }
   ul.domTree .t10 code { color: teal; }

   body.dfnEnabled dfn { cursor: pointer; }
   .dfnPanel {
     display: inline;
     position: absolute;
     z-index: 10;
     height: auto;
     width: auto;
     padding: 0.5em 0.75em;
     font: small sans-serif, Droid Sans Fallback;
     background: #DDDDDD;
     color: black;
     border: outset 0.2em;
   }
   .dfnPanel * { margin: 0; padding: 0; font: inherit; text-indent: 0; }
   .dfnPanel :link, .dfnPanel :visited { color: black; }
   .dfnPanel p { font-weight: bolder; }
   .dfnPanel * + p { margin-top: 0.25em; }
   .dfnPanel li { list-style-position: inside; }

   #configUI { position: absolute; z-index: 20; top: 10em; right: 1em; width: 11em; font-size: small; }
   #configUI p { margin: 0.5em 0; padding: 0.3em; background: #EEEEEE; color: black; border: inset thin; }
   #configUI p label { display: block; }
   #configUI #updateUI, #configUI .loginUI { text-align: center; }
   #configUI input[type=button] { display: block; margin: auto; }

   fieldset { margin: 1em; padding: 0.5em 1em; }
   fieldset > legend + * { margin-top: 0; }
   fieldset > :last-child { margin-bottom: 0; }
   fieldset p { margin: 0.5em 0; }

   .stability {
     position: fixed;
     bottom: 0;
     left: 0; right: 0;
     margin: 0 auto 0 auto !important;
    z-index: 1000;
     width: 50%;
     background: maroon; color: yellow;
     -webkit-border-radius: 1em 1em 0 0;
     -moz-border-radius: 1em 1em 0 0;
     border-radius: 1em 1em 0 0;
     -moz-box-shadow: 0 0 1em #500;
     -webkit-box-shadow: 0 0 1em #500;
     box-shadow: 0 0 1em red;
     padding: 0.5em 1em;
     text-align: center;
   }
   .stability strong {
     display: block;
   }
   .stability input {
     appearance: none; margin: 0; border: 0; padding: 0.25em 0.5em; background: transparent; color: black;
     position: absolute; top: -0.5em; right: 0; font: 1.25em sans-serif; text-align: center;
   }
   .stability input:hover {
     color: white;
     text-shadow: 0 0 2px black;
   }
   .stability input:active {
     padding: 0.3em 0.45em 0.2em 0.55em;
   }
   .stability :link, .stability :visited,
   .stability :link:hover, .stability :visited:hover {
     background: transparent;
     color: white;
   }

  </style><link href="data:text/css,.impl%20%7B%20display:%20none;%20%7D%0Ahtml%20%7B%20border:%20solid%20yellow;%20%7D%20.domintro:before%20%7B%20display:%20none;%20%7D" id="author" rel="alternate stylesheet" title="Author documentation only"><link href="data:text/css,.impl%20%7B%20background:%20%23FFEEEE;%20%7D%20.domintro:before%20%7B%20background:%20%23FFEEEE;%20%7D" id="highlight" rel="alternate stylesheet" title="Highlight implementation
requirements"><link href="http://www.w3.org/StyleSheets/TR/W3C-WD" rel="stylesheet" type="text/css"><style type="text/css">

   .applies thead th > * { display: block; }
   .applies thead code { display: block; }
   .applies tbody th { whitespace: nowrap; }
   .applies td { text-align: center; }
   .applies .yes { background: yellow; }

   .matrix, .matrix td { border: hidden; text-align: right; }
   .matrix { margin-left: 2em; }

   .dice-example { border-collapse: collapse; border-style: hidden solid solid hidden; border-width: thin; margin-left: 3em; }
   .dice-example caption { width: 30em; font-size: smaller; font-style: italic; padding: 0.75em 0; text-align: left; }
   .dice-example td, .dice-example th { border: solid thin; width: 1.35em; height: 1.05em; text-align: center; padding: 0; }

   td.eg { border-width: thin; text-align: center; }

   #table-example-1 { border: solid thin; border-collapse: collapse; margin-left: 3em; }
   #table-example-1 * { font-family: "Essays1743", serif; line-height: 1.01em; }
   #table-example-1 caption { padding-bottom: 0.5em; }
   #table-example-1 thead, #table-example-1 tbody { border: none; }
   #table-example-1 th, #table-example-1 td { border: solid thin; }
   #table-example-1 th { font-weight: normal; }
   #table-example-1 td { border-style: none solid; vertical-align: top; }
   #table-example-1 th { padding: 0.5em; vertical-align: middle; text-align: center; }
   #table-example-1 tbody tr:first-child td { padding-top: 0.5em; }
   #table-example-1 tbody tr:last-child td { padding-bottom: 1.5em; }
   #table-example-1 tbody td:first-child { padding-left: 2.5em; padding-right: 0; width: 9em; }
   #table-example-1 tbody td:first-child::after { content: leader(". "); }
   #table-example-1 tbody td { padding-left: 2em; padding-right: 2em; }
   #table-example-1 tbody td:first-child + td { width: 10em; }
   #table-example-1 tbody td:first-child + td ~ td { width: 2.5em; }
   #table-example-1 tbody td:first-child + td + td + td ~ td { width: 1.25em; }

   .apple-table-examples { border: none; border-collapse: separate; border-spacing: 1.5em 0em; width: 40em; margin-left: 3em; }
   .apple-table-examples * { font-family: "Times", serif; }
   .apple-table-examples td, .apple-table-examples th { border: none; white-space: nowrap; padding-top: 0; padding-bottom: 0; }
   .apple-table-examples tbody th:first-child { border-left: none; width: 100%; }
   .apple-table-examples thead th:first-child ~ th { font-size: smaller; font-weight: bolder; border-bottom: solid 2px; text-align: center; }
   .apple-table-examples tbody th::after, .apple-table-examples tfoot th::after { content: leader(". ") }
   .apple-table-examples tbody th, .apple-table-examples tfoot th { font: inherit; text-align: left; }
   .apple-table-examples td { text-align: right; vertical-align: top; }
   .apple-table-examples.e1 tbody tr:last-child td { border-bottom: solid 1px; }
   .apple-table-examples.e1 tbody + tbody tr:last-child td { border-bottom: double 3px; }
   .apple-table-examples.e2 th[scope=row] { padding-left: 1em; }
   .apple-table-examples sup { line-height: 0; }

   .details-example img { vertical-align: top; }

   #base64-table {
     white-space: nowrap;
     font-size: 0.6em;
     column-width: 6em;
     column-count: 5;
     column-gap: 1em;
     -moz-column-width: 6em;
     -moz-column-count: 5;
     -moz-column-gap: 1em;
     -webkit-column-width: 6em;
     -webkit-column-count: 5;
     -webkit-column-gap: 1em;
   }
   #base64-table thead { display: none; }
   #base64-table * { border: none; }
   #base64-table tbody td:first-child:after { content: ':'; }
   #base64-table tbody td:last-child { text-align: right; }

   #named-character-references-table {
     white-space: nowrap;
     font-size: 0.6em;
     column-width: 30em;
     column-gap: 1em;
     -moz-column-width: 30em;
     -moz-column-gap: 1em;
     -webkit-column-width: 30em;
     -webkit-column-gap: 1em;
   }
   #named-character-references-table > table > tbody > tr > td:first-child + td,
   #named-character-references-table > table > tbody > tr > td:last-child { text-align: center; }
   #named-character-references-table > table > tbody > tr > td:last-child:hover > span { position: absolute; top: auto; left: auto; margin-left: 0.5em; line-height: 1.2; font-size: 5em; border: outset; padding: 0.25em 0.5em; background: white; width: 1.25em; height: auto; text-align: center; }
   #named-character-references-table > table > tbody > tr#entity-CounterClockwiseContourIntegral > td:first-child { font-size: 0.5em; }

   .glyph.control { color: red; }

   @font-face {
     font-family: 'Essays1743';
     src: url('http://www.whatwg.org/specs/web-apps/current-work/fonts/Essays1743.ttf');
   }
   @font-face {
     font-family: 'Essays1743';
     font-weight: bold;
     src: url('http://www.whatwg.org/specs/web-apps/current-work/fonts/Essays1743-Bold.ttf');
   }
   @font-face {
     font-family: 'Essays1743';
     font-style: italic;
     src: url('http://www.whatwg.org/specs/web-apps/current-work/fonts/Essays1743-Italic.ttf');
   }
   @font-face {
     font-family: 'Essays1743';
     font-style: italic;
     font-weight: bold;
     src: url('http://www.whatwg.org/specs/web-apps/current-work/fonts/Essays1743-BoldItalic.ttf');
   }

  </style><style type="text/css">
   .domintro:before { display: table; margin: -1em -0.5em -0.5em auto; width: auto; content: 'This box is non-normative. Implementation requirements are given below this box.'; color: black; font-style: italic; border: solid 2px; background: white; padding: 0 0.25em; }
  </style><script type="text/javascript">
   function getCookie(name) {
     var params = location.search.substr(1).split("&");
     for (var index = 0; index < params.length; index++) {
       if (params[index] == name)
         return "1";
       var data = params[index].split("=");
       if (data[0] == name)
         return unescape(data[1]);
     }
     var cookies = document.cookie.split("; ");
     for (var index = 0; index < cookies.length; index++) {
       var data = cookies[index].split("=");
       if (data[0] == name)
         return unescape(data[1]);
     }
     return null;
   }
  </script>
  <script src="link-fixup.js" type="text/javascript"></script>
  <link href="style.css" rel="stylesheet"><link href="offline.html" title="5.6 Offline Web applications" rel="prev">
  <link href="spec.html#contents" title="Table of contents" rel="index">
  <link href="timers.html" title="6.3 Timers" rel="next">
  </head><body><div class="head" id="head">
<div id="multipage-common">
  <p class="stability" id="wip"><strong>This is a work in
  progress!</strong> For the latest updates from the HTML WG, possibly
  including important bug fixes, please look at the <a href="http://dev.w3.org/html5/spec/Overview.html">editor's draft</a> instead.
  There may also be a more
  <a href="http://www.w3.org/TR/html5">up-to-date Working Draft</a>
   with changes based on resolution of Last Call issues.
  <input onclick="closeWarning(this.parentNode)" type="button" value="&#9587;&#8413;"></p>
  <script type="text/javascript">
   function closeWarning(element) {
     element.parentNode.removeChild(element);
     var date = new Date();
     date.setDate(date.getDate()+4);
     document.cookie = 'hide-obsolescence-warning=1; expires=' + date.toGMTString();
   }
   if (getCookie('hide-obsolescence-warning') == '1')
     setTimeout(function () { document.getElementById('wip').parentNode.removeChild(document.getElementById('wip')); }, 2000);
  </script></div>

   <p><a href="http://www.w3.org/"><img alt="W3C" height="48" src="http://www.w3.org/Icons/w3c_home" width="72"></a></p>

   <h1>HTML5</h1>
   </div><div>
   <a href="offline.html" class="prev">5.6 Offline Web applications</a> &#8211;
   <a href="spec.html#contents">Table of contents</a> &#8211;
   <a href="timers.html" class="next">6.3 Timers</a>
  <ol class="toc"><li><a href="webappapis.html#webappapis"><span class="secno">6 </span>Web application APIs</a>
  <ol><li><a href="webappapis.html#scripting"><span class="secno">6.1 </span>Scripting</a>
    <ol><li><a href="webappapis.html#introduction-5"><span class="secno">6.1.1 </span>Introduction</a></li><li><a href="webappapis.html#enabling-and-disabling-scripting"><span class="secno">6.1.2 </span>Enabling and disabling scripting</a></li><li><a href="webappapis.html#processing-model-1"><span class="secno">6.1.3 </span>Processing model</a>
      <ol><li><a href="webappapis.html#definitions-0"><span class="secno">6.1.3.1 </span>Definitions</a></li><li><a href="webappapis.html#calling-scripts"><span class="secno">6.1.3.2 </span>Calling scripts</a></li><li><a href="webappapis.html#creating-scripts"><span class="secno">6.1.3.3 </span>Creating scripts</a></li><li><a href="webappapis.html#killing-scripts"><span class="secno">6.1.3.4 </span>Killing scripts</a></li><li><a href="webappapis.html#runtime-script-errors"><span class="secno">6.1.3.5 </span>Runtime script errors</a></li></ol></li><li><a href="webappapis.html#event-loops"><span class="secno">6.1.4 </span>Event loops</a>
      <ol><li><a href="webappapis.html#definitions-1"><span class="secno">6.1.4.1 </span>Definitions</a></li><li><a href="webappapis.html#processing-model-2"><span class="secno">6.1.4.2 </span>Processing model</a></li><li><a href="webappapis.html#generic-task-sources"><span class="secno">6.1.4.3 </span>Generic task sources</a></li></ol></li><li><a href="webappapis.html#javascript-protocol"><span class="secno">6.1.5 </span>The <code title="">javascript:</code> URL scheme</a></li><li><a href="webappapis.html#events"><span class="secno">6.1.6 </span>Events</a>
      <ol><li><a href="webappapis.html#event-handler-attributes"><span class="secno">6.1.6.1 </span>Event handlers</a></li><li><a href="webappapis.html#event-handlers-on-elements-document-objects-and-window-objects"><span class="secno">6.1.6.2 </span>Event handlers on elements, <code>Document</code> objects, and <code>Window</code> objects</a></li><li><a href="webappapis.html#event-firing"><span class="secno">6.1.6.3 </span>Event firing</a></li><li><a href="webappapis.html#events-and-the-window-object"><span class="secno">6.1.6.4 </span>Events and the <code>Window</code> object</a></li></ol></li></ol></li><li><a href="webappapis.html#atob"><span class="secno">6.2 </span>Base64 utility methods</a></li></ol></li></ol></div>

  <h2 id="webappapis"><span class="secno">6 </span>Web application APIs</h2><h3 id="scripting"><span class="secno">6.1 </span>Scripting</h3><h4 id="introduction-5"><span class="secno">6.1.1 </span>Introduction</h4><p>Various mechanisms can cause author-provided executable code to
  run in the context of a document. These mechanisms include, but are
  probably not limited to:</p><ul><li>Processing of <code><a href="scripting-1.html#the-script-element">script</a></code> elements.</li>

   <li>Processing of inline <code title="javascript
   protocol"><a href="#javascript-protocol">javascript:</a></code> URLs (e.g. the <code title="attr-img-src"><a href="embedded-content-1.html#attr-img-src">src</a></code> attribute of <code><a href="embedded-content-1.html#the-img-element">img</a></code>
   elements, or an <code title="">@import</code> rule in a CSS
   <code><a href="semantics.html#the-style-element">style</a></code> element block).</li>

   <li>Event handlers, whether registered through the DOM using <code title="">addEventListener()</code>, by explicit <a href="#event-handler-content-attributes">event handler
   content attributes</a>, by <a href="#event-handler-idl-attributes">event handler IDL
   attributes</a>, or otherwise.</li>

   <li>Processing of technologies like XBL or SVG that have their own
   scripting features.</li>

  </ul><div class="impl">

  <h4 id="enabling-and-disabling-scripting"><span class="secno">6.1.2 </span>Enabling and disabling scripting</h4>

  <p><dfn id="concept-bc-script" title="concept-bc-script">Scripting is enabled</dfn> in a
  <em><a href="browsers.html#browsing-context">browsing context</a></em> when all of the
  following conditions are true:</p>

  <ul><li>The user agent supports scripting.</li>

   <li>The user has not disabled scripting for this <a href="browsers.html#browsing-context">browsing
   context</a> at this time. (User agents may provide users with
   the option to disable scripting globally, or in a finer-grained
   manner, e.g. on a per-origin basis.)</li>

   <li id="sandboxScriptBlocked">The <a href="browsers.html#browsing-context">browsing context</a> did
   not have the <a href="the-iframe-element.html#sandboxed-scripts-browsing-context-flag">sandboxed scripts browsing context flag</a>
   set when the <a href="browsers.html#browsing-context">browsing context</a>'s <a href="browsers.html#active-document">active
   document</a> was created.</li>

  </ul><p><dfn id="concept-bc-noscript" title="concept-bc-noscript">Scripting is disabled</dfn> in a
  <a href="browsers.html#browsing-context">browsing context</a> when any of the above conditions are
  false (i.e. when scripting is not <a href="#concept-bc-script" title="concept-bc-script">enabled</a>).</p>

  <hr><p><dfn id="concept-n-script" title="concept-n-script">Scripting is enabled</dfn> for a
  <em>node</em> if the <code><a href="infrastructure.html#document">Document</a></code> object of the node (the
  node itself, if it is itself a <code><a href="infrastructure.html#document">Document</a></code> object) has an
  associated <a href="browsers.html#browsing-context">browsing context</a>, and <a href="#concept-bc-script" title="concept-bc-script">scripting is enabled</a> in that
  <a href="browsers.html#browsing-context">browsing context</a>.</p>

  <p><dfn id="concept-n-noscript" title="concept-n-noscript">Scripting is disabled</dfn> for a
  node if there is no such <a href="browsers.html#browsing-context">browsing context</a>, or if <a href="#concept-bc-noscript" title="concept-bc-noscript">scripting is disabled</a> in that
  <a href="browsers.html#browsing-context">browsing context</a>.</p>

  </div><div class="impl">

  
  <h4 id="processing-model-1"><span class="secno">6.1.3 </span>Processing model</h4>

  <h5 id="definitions-0"><span class="secno">6.1.3.1 </span>Definitions</h5>

  <p>A <dfn id="concept-script" title="concept-script">script</dfn> has:</p>

  <dl><dt>A <dfn id="script-execution-environment">script execution environment</dfn></dt>

   <dd>

    <p>The characteristics of the script execution environment depend
    on the language, and are not defined by this specification.</p>

    <p class="example">In JavaScript, the script execution environment
    consists of the interpreter, the stack of <i>execution
    contexts</i>, the <i>global code</i> and <i>function code</i> and
    the Function objects resulting, and so forth.</p>

   </dd>

   <dt>A <dfn id="list-of-code-entry-points">list of code entry-points</dfn></dt>

   <dd>

    <p>Each code entry-point represents a block of executable code
    that the script exposes to other scripts and to the user
    agent.</p>

    <p class="example">Each Function object in a JavaScript
    <a href="#script-execution-environment">script execution environment</a> has a corresponding code
    entry-point, for instance.</p>

    <p>The main program code of the script, if any, is the
    <dfn id="initial-code-entry-point"><i>initial code entry-point</i></dfn>. Typically, the code
    corresponding to this entry-point is executed immediately after
    the script is parsed.</p>

    <p class="example">In JavaScript, this corresponds to the
    execution context of the global code.</p>

   </dd>

   <dt>A relationship with the <dfn id="script-s-global-object">script's global object</dfn></dt>

   <dd>

    <p>An object that provides the APIs that the code can use.</p>

    <p class="example">This is typically a <code><a href="browsers.html#window">Window</a></code>
    object. In JavaScript, this corresponds to the <i>global
    object</i>.</p>

    <p class="note">When a <a href="#script-s-global-object">script's global object</a> is an
    empty object, it can't do anything that interacts with the
    environment.</p>

    <p>If the <a href="#script-s-global-object">script's global object</a> is a
    <code><a href="browsers.html#window">Window</a></code> object, then in JavaScript, the ThisBinding of
    the global execution context for this script must be the
    <code><a href="browsers.html#window">Window</a></code> object's <code><a href="browsers.html#windowproxy">WindowProxy</a></code> object,
    rather than the global object. <a href="references.html#refsECMA262">[ECMA262]</a></p>

    <p class="note">This is a <a href="introduction.html#willful-violation">willful violation</a> of the
    JavaScript specification current at the time of writing
    (ECMAScript edition 5, as defined in section 10.4.1.1 Initial
    Global Execution Context, step 3). The JavaScript specification
    requires that the <code title="">this</code> keyword in the global
    scope return the global object, but this is not compatible with
    the security design prevalent in implementations as specified
    herein. <a href="references.html#refsECMA262">[ECMA262]</a></p>

   </dd>

   <dt>A relationship with the <dfn id="script-s-browsing-context">script's browsing context</dfn></dt>

   <dd>

    <p>A <a href="browsers.html#browsing-context">browsing context</a> that is assigned responsibility
    for actions taken by the script.</p>

    <p class="example">When a script creates and <a href="history.html#navigate" title="navigate">navigates</a> a new <a href="browsers.html#top-level-browsing-context">top-level browsing
    context</a>, the <code title="dom-opener"><a href="browsers.html#dom-opener">opener</a></code>
    attribute of the new <a href="browsers.html#browsing-context">browsing context</a>'s
    <code><a href="browsers.html#window">Window</a></code> object will be set to the <a href="#script-s-browsing-context">script's
    browsing context</a>'s <code><a href="browsers.html#windowproxy">WindowProxy</a></code> object.</p>

   </dd>

   <dt>A relationship with the <dfn id="script-s-document">script's document</dfn></dt>

   <dd>

    <p>A <code><a href="infrastructure.html#document">Document</a></code> that is assigned responsibility for
    actions taken by the script.</p>

    <p class="example">When a script <a href="fetching-resources.html#fetch" title="fetch">fetches</a> a resource, the <a href="dom.html#the-document-s-current-address" title="the
    document's current address">current address</a> of the
    <a href="#script-s-document">script's document</a> will be used to set the <code title="http-referer">Referer</code> (sic) header.</p>

   </dd>

   <dt>A <dfn id="script-s-url-character-encoding" title="script's URL character encoding">URL character encoding</dfn></dt>

   <dd>

    <p>A character encoding, set when the script is created, used to
    encode URLs. <span id="sce-not-copy" title="">If the character
    encoding is set from another source, e.g. a <a href="dom.html#document-s-character-encoding">document's
    character encoding</a>, then the <a href="#script-s-url-character-encoding">script's URL character
    encoding</a> must follow the source, so that if the source's
    changes, so does the script's.</span></p>

   </dd>

   <dt>A <dfn id="script-s-base-url" title="script's base URL">base URL</dfn></dt>

   <dd>

    <p>A <a href="urls.html#url">URL</a>, set when the script is created, used to
    resolve relative URLs. <span id="sbu-not-copy" title="">If the
    base URL is set from another source, e.g. a <a href="urls.html#document-base-url">document base
    URL</a>, then the <a href="#script-s-base-url">script's base URL</a> must follow
    the source, so that if the source's changes, so does the
    script's.</span></p>

   </dd>

  </dl></div><div class="impl">

  <h5 id="calling-scripts"><span class="secno">6.1.3.2 </span>Calling scripts</h5>

  <p>When a user agent is to <dfn id="jump-to-a-code-entry-point">jump to a code entry-point</dfn> for
  a <a href="#concept-script" title="concept-script">script</a>, for example to invoke
  an event listener defined in that <a href="#concept-script" title="concept-script">script</a>, the user agent must run the
  following steps:</p>

  <ol><li><p>If the <a href="#script-s-global-object">script's global object</a> is a
   <code><a href="browsers.html#window">Window</a></code> object whose <code><a href="infrastructure.html#document">Document</a></code> object is
   not <a href="browsers.html#fully-active">fully active</a>, then abort these steps without doing
   anything. The callback is not fired.</p>

   </li><li><p>Set the <a href="browsers.html#entry-script">entry script</a> to be the <a href="#concept-script" title="concept-script">script</a> being invoked.</p></li>

   <li><p>Make the <a href="#script-execution-environment" title="script execution environment">script
   execution environment</a> for the <a href="#concept-script" title="concept-script">script</a> execute the code for the given
   code entry-point.</p></li>

   <li><p>Set the <a href="browsers.html#entry-script">entry script</a> back to whatever it was
   when this algorithm started.</p></li>

  </ol><p>This algorithm is not invoked by one script calling another.</p>

  </div><div class="impl">

  <h5 id="creating-scripts"><span class="secno">6.1.3.3 </span>Creating scripts</h5>

  <p>When the specification says that a <a href="#concept-script" title="concept-script">script</a> is to be <dfn id="create-a-script" title="create a
  script">created</dfn>, given some script source, its scripting
  language, a global object, a browsing context, a URL character
  encoding, and a base URL, the user agent must run the following
  steps:</p>

  <ol><li><p>If <a href="#concept-bc-noscript" title="concept-bc-noscript">scripting is
   disabled</a> for <a href="browsers.html#browsing-context">browsing context</a> passed to this
   algorithm, then abort these steps, as if the script did nothing but
   return void.</p>

   </li><li><p>Set up a <a href="#script-execution-environment">script execution environment</a> as
   appropriate for the scripting language.</p></li>

   <li><p>Parse/compile/initialize the source of the script using the
   <a href="#script-execution-environment">script execution environment</a>, as appropriate for the
   scripting language, and thus obtain the <a href="#list-of-code-entry-points">list of code
   entry-points</a> for the script. If the semantics of the
   scripting language and the given source code are such that there is
   executable code to be immediately run, then the <i><a href="#initial-code-entry-point">initial code
   entry-point</a></i> is the entry-point for that code.</p></li>

   <li><p>Set up the <a href="#script-s-global-object">script's global object</a>, the
   <a href="#script-s-browsing-context">script's browsing context</a>, the <a href="#script-s-document">script's
   document</a>, the <a href="#script-s-url-character-encoding">script's URL character encoding</a>,
   and the <a href="#script-s-base-url">script's base URL</a> from the settings passed to
   this algorithm.</p></li>

   <li>
 
    <p>If all the steps above succeeded (in particular, if the script
    was compiled successfully), <a href="#jump-to-a-code-entry-point" title="jump to a code
    entry-point">Jump</a> to the <a href="#concept-script" title="concept-script">script</a>'s <i><a href="#initial-code-entry-point">initial code
    entry-point</a></i>.</p>

    <p>Otherwise, <a href="#report-the-error">report the error</a> using the <code title="handler-window-onerror"><a href="#handler-window-onerror">onerror</a></code> <a href="#event-handlers" title="event
    handlers">event handler</a> of the <a href="#script-s-global-object">script's global
    object</a>. If the error is still <i title="concept-error-nothandled"><a href="#concept-error-nothandled">not handled</a></i> after this, then
    the error may be reported to the user.</p>

   </li>

  </ol><hr><p>When the user agent is to <dfn id="create-an-impotent-script">create an impotent script</dfn>,
  given some script source, its scripting language, and a browsing
  context, the user agent must <a href="#create-a-script">create a script</a>, using the
  given script source and scripting language, using a new empty object
  as the global object, and using the given browsing context as the
  browsing context. The URL character encoding and base URL for the
  resulting <a href="#concept-script" title="concept-script">script</a> are not
  important as no APIs are exposed to the script.</p>

  <hr><p>When the specification says that a <a href="#concept-script" title="concept-script">script</a> is to be <dfn id="create-a-script-from-a-node" title="create a
  script from a node">created from a node</dfn> <var title="">node</var>, given some script source and its scripting
  language, the user agent must <a href="#create-a-script">create a script</a>, using
  the given script source and scripting language, and using <a href="#the-script-settings-determined-from-the-node">the
  script settings determined from the node</a> <var title="">node</var>.</p>

  <p><dfn id="the-script-settings-determined-from-the-node">The script settings determined from the node</dfn> <var title="">node</var> are computed as follows:</p>

  <ol><li><p>Let <var title="">document</var> be the
   <code><a href="infrastructure.html#document">Document</a></code> of <var title="">node</var> (or <var title="">node</var> itself if it is a
   <code><a href="infrastructure.html#document">Document</a></code>).</p></li>

   <li><p>The browsing context is the <a href="browsers.html#browsing-context">browsing context</a> of
   <var title="">document</var>.</p>

   </li><li><p>The global object is the <code><a href="browsers.html#window">Window</a></code> object of
   <var title="">document</var>.</p></li>

   <li><p>The URL character encoding is the <a href="dom.html#document-s-character-encoding" title="document's
   character encoding">character encoding</a> of <var title="">document</var>. (<a href="#sce-not-copy">This is a
   reference, not a copy</a>.)</p></li>

   <li><p>The base URL is the <a href="urls.html#document-base-url" title="document base URL">base
   URL</a> of <var title="">document</var>. (<a href="#sbu-not-copy">This is a reference, not a copy</a>.)</p></li>

  </ol></div><div class="impl">

  <h5 id="killing-scripts"><span class="secno">6.1.3.4 </span>Killing scripts</h5>

  <p>User agents may impose resource limitations on scripts, for
  example CPU quotas, memory limits, total execution time limits, or
  bandwidth limitations. When a script exceeds a limit, the user agent
  may either throw a <code><a href="common-dom-interfaces.html#quota_exceeded_err">QUOTA_EXCEEDED_ERR</a></code> exception, abort
  the script without an exception, prompt the user, or throttle script
  execution.</p>

  <div class="example">

   <p>For example, the following script never terminates. A user agent
   could, after waiting for a few seconds, prompt the user to either
   terminate the script or let it continue.</p>

   <pre>&lt;script&gt;
 while (true) { /* loop */ }
&lt;/script&gt;</pre>

  </div>

  <p>User agents are encouraged to allow users to disable scripting
  whenever the user is prompted either by a script (e.g. using the
  <code title="dom-alert"><a href="timers.html#dom-alert">window.alert()</a></code> API) or because of a
  script's actions (e.g. because it has exceeded a time limit).</p>

  <p>If scripting is disabled while a script is executing, the script
  should be terminated immediately.</p>

  </div><div class="impl">

  <h5 id="runtime-script-errors"><span class="secno">6.1.3.5 </span>Runtime script errors</h5>

  <p>Whenever an uncaught runtime script error occurs in one of the
  scripts associated with a <code><a href="infrastructure.html#document">Document</a></code>, the user agent must
  <a href="#report-the-error">report the error</a> using the <code title="handler-window-onerror"><a href="#handler-window-onerror">onerror</a></code> <a href="#event-handlers" title="event
  handlers">event handler</a> of the <a href="#script-s-global-object">script's global
  object</a>. If the error is still <i title="concept-error-nothandled"><a href="#concept-error-nothandled">not handled</a></i> after this, then
  the error may be reported to the user.</p>

  <hr><p>When the user agent is required to <dfn id="report-the-error" title="report the
  error">report an error</dfn> <var title="">error</var> using the
  <a href="#event-handlers" title="event handlers">event handler</a> <var title="">onerror</var>, it must run these steps, after which the
  error is either <dfn id="concept-error-handled" title="concept-error-handled"><i>handled</i></dfn> or <dfn id="concept-error-nothandled" title="concept-error-nothandled"><i>not handled</i></dfn>:</p>

  <dl class="switch"><dt>If the value of <var title="">onerror</var> is a
   <code><a href="#function">Function</a></code></dt>

   <dd>

    <p>The function must be invoked with three arguments. The three
    arguments passed to the function are all <code>DOMString</code>s;
    the first must give the message that the UA is considering
    reporting, the second must give the <a href="urls.html#absolute-url">absolute URL</a> of
    the resource in which the error occurred, and the third must give
    the line number in that resource on which the error occurred.</p>

    <p>If the function returns false, then the error is <i title="concept-error-handled"><a href="#concept-error-handled">handled</a></i>. Otherwise, the error is
    <i title="concept-error-nothandled"><a href="#concept-error-nothandled">not handled</a></i>.</p>

    <p>Any uncaught exceptions thrown or errors caused by this
    function may be reported to the user immediately after the error
    that the function was called for; the <a href="#report-the-error" title="report the
    error">report an error</a> algorithm must not be used to handle
    exceptions thrown or errors caused by this function.</p>

   </dd>

   <dt>Otherwise</dt>

   <dd>

    <p>The error is <i title="concept-error-nothandled"><a href="#concept-error-nothandled">not handled</a></i>.</p>

   </dd>

  </dl></div><div class="impl">

  <h4 id="event-loops"><span class="secno">6.1.4 </span>Event loops</h4>

  <h5 id="definitions-1"><span class="secno">6.1.4.1 </span>Definitions</h5>

  <p>To coordinate events, user interaction, scripts, rendering,
  networking, and so forth, user agents must use <dfn id="event-loop" title="event
  loop">event loops</dfn> as described in this section.</p>

  <p>There must be at least one <a href="#event-loop">event loop</a> per user
  agent, and at most one <a href="#event-loop">event loop</a> per <a href="browsers.html#unit-of-related-similar-origin-browsing-contexts">unit of
  related similar-origin browsing contexts</a>.</p>

  <p class="note">When there is more than one <a href="#event-loop">event loop</a>
  for a <a href="browsers.html#unit-of-related-browsing-contexts">unit of related browsing contexts</a>, complications
  arise when a <a href="browsers.html#browsing-context">browsing context</a> in that group is <a href="history.html#navigate" title="navigate">navigated</a> such that it switches from one
  <a href="browsers.html#unit-of-related-similar-origin-browsing-contexts">unit of related similar-origin browsing contexts</a> to
  another. This specification does not currently describe how to
  handle these complications.</p>

  <p>An <a href="#event-loop">event loop</a> always has at least one <a href="browsers.html#browsing-context">browsing
  context</a>. If an <a href="#event-loop">event loop</a>'s <a href="browsers.html#browsing-context" title="browsing context">browsing contexts</a> all go away, then
  the <a href="#event-loop">event loop</a> goes away as well. A <a href="browsers.html#browsing-context">browsing
  context</a> always has an <a href="#event-loop">event loop</a> coordinating
  its activities.</p>

  
  <p class="note">Other specifications can define new kinds of event
  loops that aren't associated with browsing contexts; in particular,
  the Web Workers specification does so.</p>
  

  <p>An <a href="#event-loop">event loop</a> has one or more <dfn id="task-queue" title="task
  queue">task queues</dfn>. A <a href="#task-queue">task queue</a> is an ordered
  list of <dfn id="concept-task" title="concept-task">tasks</dfn>, which can be:</p>

  <dl><dt>Events</dt>

   <dd>

    <p>Asynchronously dispatching an <code><a href="infrastructure.html#event">Event</a></code> object at a
    particular <code><a href="infrastructure.html#eventtarget">EventTarget</a></code> object is a task.</p>

    <p class="note">Not all events are dispatched using the <a href="#task-queue">task
    queue</a>, many are dispatched synchronously during other
    tasks.</p>

   </dd>


   <dt>Parsing</dt>

   <dd><p>The <a href="parsing.html#html-parser">HTML parser</a> tokenizing one or more bytes,
   and then processing any resulting tokens, is typically a
   task.</p></dd>


   <dt>Callbacks</dt>

   <dd><p>Calling a callback asynchronously is a task.</p></dd>


   <dt>Using a resource</dt>

   <dd><p>When an algorithm <a href="fetching-resources.html#fetch" title="fetch">fetches</a> a
   resource, if the fetching occurs asynchronously then the processing
   of the resource once some or all of the resource is available is a
   task.</p></dd>


   <dt>Reacting to DOM manipulation</dt>

   <dd><p>Some elements have tasks that trigger in response to DOM
   manipulation, e.g. when that element is <a href="infrastructure.html#insert-an-element-into-a-document" title="insert an
   element into a document">inserted into the document</a>.</p>

  </dd></dl><p>When a user agent is to <dfn id="queue-a-task">queue a task</dfn>, it must add the
  given task to one of the <a href="#task-queue" title="task queue">task queues</a>
  of the relevant <a href="#event-loop">event loop</a>. All the tasks from one
  particular <dfn id="task-source">task source</dfn> (e.g. the callbacks generated by
  timers, the events dispatched for mouse movements, the tasks queued
  for the parser) must always be added to the same <a href="#task-queue">task
  queue</a>, but tasks from different <a href="#task-source" title="task
  source">task sources</a> may be placed in different <a href="#task-queue" title="task queue">task queues</a>.</p>

  <p class="example">For example, a user agent could have one
  <a href="#task-queue">task queue</a> for mouse and key events (the <a href="#user-interaction-task-source">user
  interaction task source</a>), and another for everything
  else. The user agent could then give keyboard and mouse events
  preference over other tasks three quarters of the time, keeping the
  interface responsive but not starving other task queues, and never
  processing events from any one <a href="#task-source">task source</a> out of
  order.</p>

  <p>Each <a href="#concept-task" title="concept-task">task</a> that is <a href="#queue-a-task" title="queue a task">queued</a> onto a <a href="#task-queue">task queue</a> of
  an <a href="#event-loop">event loop</a> defined by this specification is
  associated with a <code><a href="infrastructure.html#document">Document</a></code>; if the task was queued in
  the context of an element, then it is the element's
  <code><a href="infrastructure.html#document">Document</a></code>; if the task was queued in the context of a
  <a href="browsers.html#browsing-context">browsing context</a>, then it is the <a href="browsers.html#browsing-context">browsing
  context</a>'s <a href="browsers.html#active-document">active document</a> at the time the task
  was queued; if the task was queued by or for a <a href="#concept-script" title="concept-script">script</a> then the document is the
  <a href="#script-s-document">script's document</a>.</p>

  <p>A user agent is required to have one <dfn id="storage-mutex">storage
  mutex</dfn>. This mutex is used to control access to shared state
  like cookies. At any one point, the <a href="#storage-mutex">storage mutex</a> is
  either free, or owned by a particular <a href="#event-loop">event loop</a> or
  instance of the <a href="fetching-resources.html#fetch" title="fetch">fetching</a> algorithm.</p>

  <p>Whenever a <a href="#concept-script" title="concept-script">script</a> calls into
  a <a href="infrastructure.html#plugin">plugin</a>, and whenever a <a href="infrastructure.html#plugin">plugin</a> calls into
  a <a href="#concept-script" title="concept-script">script</a>, the user agent must
  release the <a href="#storage-mutex">storage mutex</a>.</p>


  <h5 id="processing-model-2"><span class="secno">6.1.4.2 </span>Processing model</h5>

  <p>An <a href="#event-loop">event loop</a> must continually run through the
  following steps for as long as it exists:</p>

  <ol><li><p>Run the oldest <a href="#concept-task" title="concept-task">task</a> on one
   of the <a href="#event-loop">event loop</a>'s <a href="#task-queue" title="task queue">task
   queues</a>, ignoring tasks whose associated
   <code><a href="infrastructure.html#document">Document</a></code>s are not <a href="browsers.html#fully-active">fully active</a>. The user
   agent may pick any <a href="#task-queue">task queue</a>.</p></li>

   
   <li><p>If the <a href="#storage-mutex">storage mutex</a> is now owned by the
   <a href="#event-loop">event loop</a>, release it so that it is once again
   free.</p></li>

   <li><p>Remove that task from its <a href="#task-queue">task queue</a>.</p></li>

   <li><p><a href="#provide-a-stable-state">Provide a stable state</a>.</p></li>

   <li><p>If necessary, update the rendering or user interface of any
   <code><a href="infrastructure.html#document">Document</a></code> or <a href="browsers.html#browsing-context">browsing context</a> to reflect
   the current state.</p></li>

   <li><p>Return to the first step of the <a href="#event-loop">event
   loop</a>.</p></li>

  </ol><hr><p>When the user agent is to <dfn id="provide-a-stable-state">provide a stable state</dfn>, if
  any asynchronously-running algorithms are <dfn id="await-a-stable-state" title="await a stable
  state">awaiting a stable state</dfn>, then the user agent must run
  their <dfn id="synchronous-section">synchronous section</dfn> and then resume running their
  asynchronous algorithm (if appropriate).</p>

  <p class="note">A <a href="#synchronous-section">synchronous section</a> never mutates
  the DOM, runs any script, or has any other side-effects.</p>

  <p class="note">Steps in <a href="#synchronous-section" title="synchronous
  section">synchronous sections</a> are marked with &#8987;.</p>

  <hr><p>When an algorithm says to <dfn id="spin-the-event-loop">spin the event loop</dfn> until
  a condition <var title="">goal</var> is met, the user agent must run
  the following steps:</p>

  <ol><li><p>Let <var title="">task source</var> be the <a href="#task-source">task
   source</a> of the currently running <a href="#concept-task" title="concept-task">task</a>.</p></li>

   <li>

    <p>Stop the currently running <a href="#concept-task" title="concept-task">task</a>, allowing the <a href="#event-loop">event
    loop</a> to resume, but continue these steps
    asynchronously.</p>

    <p class="note">This causes the <a href="#event-loop">event loop</a> to move on
    to the second step of its processing model (defined above).</p>

   </li>

   <li><p>Wait until the condition <var title="">goal</var> is
   met.</p></li>

   <li><p><a href="#queue-a-task">Queue a task</a> to continue running these steps,
   using the <a href="#task-source">task source</a> <var title="">task
   source</var>. Wait until this task runs before continuing these
   steps.</p></li>

   <li><p>Return to the caller.</p></li>

  </ol><hr><p>Some of the algorithms in this specification, for historical
  reasons, require the user agent to <dfn id="pause">pause</dfn> while running a
  <a href="#concept-task" title="concept-task">task</a> until a condition <var title="">goal</var> is met. This means running the following
  steps:</p>

  <ol><li><p>If any asynchronously-running algorithms are <a href="#await-a-stable-state" title="await a stable state">awaiting a stable state</a>, then
   run their <a href="#synchronous-section">synchronous section</a> and then resume running
   their asynchronous algorithm. (See the <a href="#event-loop">event loop</a>
   processing model definition above for details.)</p>

   </li><li><p>If necessary, update the rendering or user interface of any
   <code><a href="infrastructure.html#document">Document</a></code> or <a href="browsers.html#browsing-context">browsing context</a> to reflect
   the current state.</p></li>

   <li><p>Wait until the condition <var title="">goal</var> is met.
   While a user agent has a paused <a href="#concept-task" title="concept-task">task</a>, the corresponding <a href="#event-loop">event
   loop</a> must not run further <a href="#concept-task" title="concept-task">tasks</a>, and any script in the currently
   running <a href="#concept-task" title="concept-task">task</a> must block. User
   agents should remain responsive to user input while paused,
   however, albeit in a reduced capacity since the <a href="#event-loop">event
   loop</a> will not be doing anything.</p></li>

  </ol><hr><p>When a user agent is to <dfn id="obtain-the-storage-mutex">obtain the storage mutex</dfn> as
  part of running a <a href="#concept-task" title="concept-task">task</a>, it must
  run through the following steps:</p>

  <ol><li><p>If the <a href="#storage-mutex">storage mutex</a> is already owned by this
   <a href="#concept-task" title="concept-task">task</a>'s <a href="#event-loop">event loop</a>,
   then abort these steps.</p></li>

   <li><p>Otherwise, <a href="#pause">pause</a> until the <a href="#storage-mutex">storage
   mutex</a> can be taken by the <a href="#event-loop">event loop</a>.</p></li>

   <li><p>Take ownership of the <a href="#storage-mutex">storage mutex</a>.</p></li>

  </ol></div><div class="impl">

  <h5 id="generic-task-sources"><span class="secno">6.1.4.3 </span>Generic task sources</h5>

  <p>The following <a href="#task-source" title="task source">task sources</a> are
  used by a number of mostly unrelated features in this and other
  specifications.</p>

  <dl><dt>The <dfn id="dom-manipulation-task-source">DOM manipulation task source</dfn></dt>

   <dd>

    <p>This <a href="#task-source">task source</a> is used for features that react
    to DOM manipulations, such as things that happen asynchronously
    when an element is <a href="infrastructure.html#insert-an-element-into-a-document" title="insert an element into a
    document">inserted into the document</a>.</p>

    
   </dd>

   <dt>The <dfn id="user-interaction-task-source">user interaction task source</dfn></dt>

   <dd>

    <p>This <a href="#task-source">task source</a> is used for features that react
    to user interaction, for example keyboard or mouse input.</p>

    <p>Asynchronous events sent in response to user input (e.g. <code title="event-click"><a href="infrastructure.html#event-click">click</a></code> events) must be dispatched using
    <a href="#concept-task" title="concept-task">tasks</a> <a href="#queue-a-task" title="queue a
    task">queued</a> with the <a href="#user-interaction-task-source">user interaction task
    source</a>. <a href="references.html#refsDOMEVENTS">[DOMEVENTS]</a></p>

   </dd>

   <dt>The <dfn id="networking-task-source">networking task source</dfn></dt>

   <dd>

    <p>This <a href="#task-source">task source</a> is used for features that trigger
    in response to network activity.</p>

    

   </dd>

   <dt>The <dfn id="history-traversal-task-source">history traversal task source</dfn></dt>

   <dd>

    <p>This <a href="#task-source">task source</a> is used to queue calls to <code title="dom-history-back"><a href="history.html#dom-history-back">history.back()</a></code> and similar
    APIs.</p>

   </dd>

  </dl></div><div class="impl">

  <!-- SCRIPT EXEC -->
  <h4 id="javascript-protocol"><span class="secno">6.1.5 </span><dfn title="javascript protocol">The <code title="">javascript:</code> URL scheme</dfn></h4>

  <p>When a <a href="urls.html#url">URL</a> using the <code title="">javascript:</code> scheme is <dfn id="concept-js-deref" title="concept-js-deref">dereferenced</dfn>, the user agent must run
  the following steps:</p>

  <ol><li><p>Let the script source be the string obtained using the
   content retrieval operation defined for <code title="">javascript:</code> URLs. <a href="references.html#refsJSURL">[JSURL]</a></p></li>

   <li>

    <p>Use the appropriate step from the following list:</p>

    <dl><dt>If a <a href="browsers.html#browsing-context">browsing context</a> is being <a href="history.html#navigate" title="navigate">navigated</a> to a <code>javascript:</code>
     URL, and the <a href="history.html#source-browsing-context">source browsing context</a> for that
     navigation, if any, has <a href="#concept-bc-noscript" title="concept-bc-noscript">scripting disabled</a></dt>

     <dd>

      <p>Let <var title="">result</var> be void.</p>

     </dd>

     <dt>If a <a href="browsers.html#browsing-context">browsing context</a> is being <a href="history.html#navigate" title="navigate">navigated</a> to a <code>javascript:</code>
     URL, and the <a href="browsers.html#active-document">active document</a> of that browsing
     context has the <a href="origin-0.html#same-origin">same origin</a> as the script given by
     that URL</dt>

     <dd>

      

      <p>Let <var title="">address</var> be the <a href="dom.html#the-document-s-address" title="the
      document's address">address</a> of the <a href="browsers.html#active-document">active
      document</a> of the <a href="browsers.html#browsing-context">browsing context</a> being
      navigated.</p>

      <p>If <var title="">address</var> is <code><a href="fetching-resources.html#about:blank">about:blank</a></code>,
      and the <a href="browsers.html#browsing-context">browsing context</a> being navigated has a
      <a href="browsers.html#creator-browsing-context">creator browsing context</a>, then let <var title="">address</var> be the <a href="dom.html#the-document-s-address" title="the document's
      address">address</a> of the <a href="browsers.html#creator-document">creator
      <code>Document</code></a> instead.</p>

      <p><a href="#create-a-script-from-a-node" title="create a script from a node">Create a
      script</a> from the <code><a href="infrastructure.html#document">Document</a></code> node of the
      <a href="browsers.html#active-document">active document</a>, using the aforementioned script
      source, and assuming the scripting language is JavaScript.</p>

      <p>Let <var title="">result</var> be the return value of the
      <i><a href="#initial-code-entry-point">initial code entry-point</a></i> of this <a href="#concept-script" title="concept-script">script</a>. If an exception was
      raised, let <var title="">result</var> be void instead. (The
      result will be void also if <a href="#concept-bc-noscript" title="concept-bc-noscript">scripting is disabled</a>.)</p>

      <p>When it comes time to <a href="history.html#set-the-document-s-address">set the document's address</a>
      in the <a href="history.html#navigate" title="navigate">navigation algorithm</a>, use
      <var title="">address</var> as the <a href="history.html#override-url">override
      URL</a>.</p>

     </dd>


     <dt>Otherwise</dt>

     <dd>

      <p>Let <var title="">result</var> be void.</p>

     </dd>

    </dl></li>

   <li>

    <p>If the result of executing the script is void (there is no
    return value), then the URL must be treated in a manner equivalent
    to an HTTP resource with an HTTP 204 No Content response.</p>

    <p>Otherwise, the URL must be treated in a manner equivalent to an
    HTTP resource with a 200 OK response whose <a href="fetching-resources.html#content-type" title="Content-Type">Content-Type metadata</a> is
    <code><a href="iana.html#text-html">text/html</a></code> and whose response body is the return value
    converted to a string value.</p>

    <p class="note">Certain contexts, in particular <code><a href="embedded-content-1.html#the-img-element">img</a></code>
    elements, ignore the <a href="fetching-resources.html#content-type" title="Content-Type">Content-Type
    metadata</a>.</p>

   </li>

  </ol><div class="example">

   <p>So for example a <code title="">javascript:</code> URL for a
   <code title="attr-img-src"><a href="embedded-content-1.html#attr-img-src">src</a></code> attribute of an
   <code><a href="embedded-content-1.html#the-img-element">img</a></code> element would be evaluated in the context of an
   empty object as soon as the attribute is set; it would then be
   sniffed to determine the image type and decoded as an image.</p>

   <p>A <code title="">javascript:</code> URL in an <code title="attr-hyperlink-href"><a href="links.html#attr-hyperlink-href">href</a></code> attribute of an <code><a href="text-level-semantics.html#the-a-element">a</a></code>
   element would only be evaluated when the link was <a href="links.html#following-hyperlinks" title="following hyperlinks">followed</a>.</p>

   <p>The <code title="attr-iframe-src"><a href="the-iframe-element.html#attr-iframe-src">src</a></code> attribute of an
   <code><a href="the-iframe-element.html#the-iframe-element">iframe</a></code> element would be evaluated in the context of
   the <code><a href="the-iframe-element.html#the-iframe-element">iframe</a></code>'s own <a href="browsers.html#browsing-context">browsing context</a>; once
   evaluated, its return value (if it was not void) would replace that
   <a href="browsers.html#browsing-context">browsing context</a>'s document, thus changing the
   variables visible in that <a href="browsers.html#browsing-context">browsing context</a>.</p>

  </div>

  </div><h4 id="events"><span class="secno">6.1.6 </span>Events</h4><div class="impl">

  <h5 id="event-handler-attributes"><span class="secno">6.1.6.1 </span>Event handlers</h5>

  </div><p>Many objects can have <dfn id="event-handlers">event handlers</dfn> specified. These
  act as bubbling event listeners for the object on which they are
  specified.</p><p>An <a href="#event-handlers" title="event handlers">event handler</a> can either
  have the value null or be set to a <code><a href="#function">Function</a></code>
  object. <span class="impl">Initially, event handlers must be set to
  null.</span></p><p>Event handlers are exposed in one or two ways.</p><p>The first way, common to all event handlers, is as an <a href="#event-handler-idl-attributes" title="event handler IDL attributes">event handler IDL
  attribute</a>.</p><p>The second way is as an <a href="#event-handler-content-attributes" title="event handler content
  attributes">event handler content attribute</a>. Event handlers
  on <a href="infrastructure.html#html-elements">HTML elements</a> and some of the event handlers on
  <code><a href="browsers.html#window">Window</a></code> objects are exposed in this way.</p><div class="impl">

  <hr><p><dfn id="event-handler-idl-attributes">Event handler IDL attributes</dfn>, on setting, must set the
  corresponding event handler to their new value, and on
  getting, must return whatever the current value of the corresponding
  event handler is (possibly null).</p>

  <p>If an <a href="#event-handler-idl-attributes" title="event handler IDL attributes">event handler
  IDL attribute</a> exposes an <a href="#event-handlers" title="event handlers">event
  handler</a> of an object that doesn't exist, it must always
  return null on getting and must do nothing on setting.</p>

  <p class="note">This can happen in particular for <a href="#event-handler-idl-attributes" title="event
  handler IDL attributes">event handler IDL attribute</a> on
  <code><a href="sections.html#the-body-element">body</a></code> elements that do not have corresponding
  <code><a href="browsers.html#window">Window</a></code> objects.</p>

  <p class="note">Certain event handler IDL attributes have additional
  requirements, in particular the <code title="handler-MessagePort-onmessage">onmessage</code> attribute of
  <code>MessagePort</code> objects.</p>

  <hr></div><p><dfn id="event-handler-content-attributes">Event handler content attributes</dfn>, when specified, must
  contain valid JavaScript code which, when parsed, would match the
  <code title="">FunctionBody</code> production after automatic
  semicolon insertion. <a href="references.html#refsECMA262">[ECMA262]</a></p><div class="impl">

  <!-- SCRIPT EXEC -->
  <p>When an <a href="#event-handler-content-attributes" title="event handler content attributes">event
  handler content attribute</a> is set, if the element is owned by
  a <code><a href="infrastructure.html#document">Document</a></code> that is in a <a href="browsers.html#browsing-context">browsing context</a>,
  and <a href="#concept-bc-script" title="concept-bc-script">scripting is enabled</a> for
  that <a href="browsers.html#browsing-context">browsing context</a>, the user agent must run the
  following steps to create a <a href="#concept-script" title="concept-script">script</a> after setting the content
  attribute to its new value:</p>

  <ol><li><p>Set the corresponding <a href="#event-handlers" title="event handlers">event
   handler</a> to null.</p></li>

   <li><p>Set up a <a href="#script-execution-environment">script execution environment</a> for
   JavaScript.</p></li>

   <li><p>Let <var title="">body</var> be the <a href="#event-handler-content-attributes" title="event
   handler content attributes">event handler content
   attribute</a>'s new value.</p></li>

   <li>

    <p>If <var title="">body</var> is not parsable as
    <i>FunctionBody</i> or if parsing detects an <i>early error</i>
    then abort these steps.</p>

    <p class="note"><i>FunctionBody</i> is defined in ECMAScript
    edition 5 section 13 Function Definition. <i>Early error</i> is
    defined in ECMAScript edition 5 section 16 Errors. <a href="references.html#refsECMA262">[ECMA262]</a></p>

   </li>

   <li>

    <p>If <var title="">body</var> begins with a Directive Prologue
    that contains a Use Strict Directive then let <var title="">strict</var> be true, otherwise let <var title="">strict</var> be false.</p> 
    <p class="note">The terms "Directive Prologue" and "Use Strict
    Directive" are defined in ECMAScript edition 5 section 14.1
    Directive Prologues and the Use Strict Directive. <a href="references.html#refsECMA262">[ECMA262]</a></p>

   </li>


   <li>

    <p>Using the script execution environment created above, create a
    function object (as defined in ECMAScript edition 5 section 13.2
    Creating Function Objects), with:</p>

    <dl><dt>Parameter list <var title="">FormalParameterList</var></dt>

     <dd>

      <dl class="switch"><dt>If the attribute is the <code title="handler-window-onerror"><a href="#handler-window-onerror">onerror</a></code> attribute of the
       <code><a href="browsers.html#window">Window</a></code> object</dt>

       <dd>Let the function have three arguments, named <code title="">event</code>, <code title="">source</code>, and <code title="">fileno</code>.</dd>

       <dt>Otherwise</dt>

       <dd>Let the function have a single argument called <code title="">event</code>.</dd>

      </dl></dd>

     <dt>Function body <var title="">FunctionBody</var></dt>

     <dd>The result of parsing <var title="">body</var> above.</dd>

     <dt>Lexical Environment <var title="">Scope</var></dt>

     <dd>

      <ol><li>Let <var title="">Scope</var> be the result of
       NewObjectEnvironment(the element's <code><a href="infrastructure.html#document">Document</a></code>, the
       <var title="">global environment</var>).</li>

       <li>If the element has a <a href="association-of-controls-and-forms.html#form-owner">form owner</a>, let <var title="">Scope</var> be the result of NewObjectEnvironment(the
       element's <a href="association-of-controls-and-forms.html#form-owner">form owner</a>, <var title="">Scope</var>).</li>

       <li>Let <var title="">Scope</var> be the result of
       NewObjectEnvironment(the element's object, <var title="">Scope</var>).</li>

      </ol><p class="note">NewObjectEnvironment() is defined in ECMAScript
      edition 5 section 10.2.2.3 NewObjectEnvironment (O, E). <a href="references.html#refsECMA262">[ECMA262]</a></p>

     </dd>

     <dt>Boolean flag <var title="">Strict</var></dt>

     <dd>The value of <var title="">strict</var>.</dd>

    </dl><p>Let this new function be the only entry in the script's
    <a href="#list-of-code-entry-points">list of code entry-points</a>.</p>

   </li>

   <li><p>Set up the <a href="#script-s-global-object">script's global object</a>, the
   <a href="#script-s-browsing-context">script's browsing context</a>, the <a href="#script-s-document">script's
   document</a>, the <a href="#script-s-url-character-encoding">script's URL character encoding</a>,
   and the <a href="#script-s-base-url">script's base URL</a> from <a href="#the-script-settings-determined-from-the-node">the script
   settings determined from the node</a> on which the attribute is
   being set.</p></li>

   <li><p>Set the corresponding <a href="#event-handlers" title="event handlers">event
   handler</a> to the aforementioned function.</p></li>

  </ol><p>When an event handler content attribute is removed, the user
  agent must set the corresponding <a href="#event-handlers" title="event handlers">event
  handler</a> to null.</p>
  
  </div><p class="note">When an <a href="#event-handler-content-attributes" title="event handler content
  attributes">event handler content attribute</a> is set on an
  element owned by a <code><a href="infrastructure.html#document">Document</a></code> that is not in a
  <a href="browsers.html#browsing-context">browsing context</a>, the corresponding event handler is
  not changed.</p><div class="impl">

  <hr><p>All <a href="#event-handlers">event handlers</a> on an object, whether an element
  or some other object, and whether set to null or to a
  <code><a href="#function">Function</a></code> object, must be registered as event listeners
  on the object when it is created, as if the <code title="dom-EventTarget-addEventListener">addEventListener()</code>
  method on the object's <code><a href="infrastructure.html#eventtarget">EventTarget</a></code> interface had been
  invoked, with the event type (<var title="dom-event-type">type</var>
  argument) equal to the type corresponding to the event handler (the
  <dfn id="event-handler-event-type">event handler event type</dfn>), the listener set to be a
  target and bubbling phase listener (<var title="dom-event-useCapture">useCapture</var> argument set to
  false), and the event listener itself (<var title="dom-event-listener">listener</var> argument) set to do
  nothing while the event handler's value is not a
  <code><a href="#function">Function</a></code> object, and set to invoke the <code title="dom-function-call"><a href="#dom-function-call">call()</a></code> callback of the
  <code><a href="#function">Function</a></code> object associated with the event handler
  otherwise.</p>

  </div><p class="note"><a href="#event-handlers">Event handlers</a> <span class="impl">therefore</span> always fire before event listeners
  attached using <code title="dom-EventTarget-addEventListener">addEventListener()</code>.</p><div class="impl">

  <p class="note">The <var title="dom-event-listener">listener</var>
  argument is emphatically <em>not</em> the <a href="#event-handlers" title="event
  handlers">event handler</a> itself.</p>

  <p class="note">The interfaces implemented by the event object do
  not influence whether an <a href="#event-handlers" title="event handlers">event
  handler</a> is triggered or not.</p>

  <p>When an <a href="#event-handlers" title="event handlers">event handler</a>'s
  <code><a href="#function">Function</a></code> object is invoked, its <code title="dom-function-call"><a href="#dom-function-call">call()</a></code> callback must be invoked
  with one argument, set to the <code><a href="infrastructure.html#event">Event</a></code> object of the event
  in question.</p>

  <p>The handler's return value must then be processed as follows:</p>

  <dl class="switch"><dt>If the event type is <code class="event-mouseover">mouseover</code></dt>

   <dd><p>If the return value is a boolean with the value true, then
   the event must be canceled.</p></dd>

   <dt>If the event object is a <code><a href="history.html#beforeunloadevent">BeforeUnloadEvent</a></code> object</dt>

   <dd><p>If the return value is a string, and the event object's
   <code title="dom-BeforeUnloadEvent-returnValue"><a href="history.html#dom-beforeunloadevent-returnvalue">returnValue</a></code>
   attribute's value is the empty string, then set the <code title="dom-BeforeUnloadEvent-returnValue"><a href="history.html#dom-beforeunloadevent-returnvalue">returnValue</a></code>
   attribute's value to the return value.</p></dd>

   <dt>Otherwise</dt>

   <dd><p>If the return value is a boolean with the value false, then
   the event must be canceled.</p></dd>

  </dl></div><hr><p>The <code><a href="#function">Function</a></code> interface represents a function in the
  scripting language being used. It is represented in IDL as
  follows:</p><pre class="idl">[Callback=FunctionOnly, NoInterfaceObject]
interface <dfn id="function">Function</dfn> {
  any <a href="#dom-function-call" title="dom-function-call">call</a>(in any... arguments);
};</pre><p>The <dfn id="dom-function-call" title="dom-function-call"><code>call(...)</code></dfn>
  method is the object's callback.</p><p class="note">In JavaScript, any <code title="">Function</code>
  object implements this interface.</p><p>If the <code><a href="#function">Function</a></code> object is a JavaScript <code title="">Function</code>, then when it is invoked by the user agent,
  the user agent must set the <var title="">thisArg</var> (as defined
  by ECMAScript edition 5 section 10.4.3 Entering Function Code) to
  the <a href="#event-handlers" title="event handlers">event handler</a>'s object. <a href="references.html#refsECMA262">[ECMA262]</a></p><div class="example">

   <p>For example, the following document fragment:</p>

   <pre>&lt;body onload="alert(this)" onclick="alert(this)"&gt;</pre>

   <p>...leads to an alert saying "<code title="">[object&#160;Window]</code>" when the document is loaded,
   and an alert saying "<code title="">[object&#160;HTMLBodyElement]</code>" whenever the user
   clicks something in the page.</p>

  </div><p>The return value of the function affects whether the event is
  canceled or not: <span class="impl">as described above,</span> if
  the return value is false, the event is canceled (except for <code class="event-mouseover">mouseover</code> events, where the return
  value has to be true to cancel the event). With <code title="event-beforeunload">beforeunload</code> events, the value is
  instead used to determine the message to show the user.</p><div class="impl">

  <h5 id="event-handlers-on-elements-document-objects-and-window-objects"><span class="secno">6.1.6.2 </span>Event handlers on elements, <code><a href="infrastructure.html#document">Document</a></code> objects, and <code><a href="browsers.html#window">Window</a></code> objects</h5>

  <p>The following are the <a href="#event-handlers">event handlers</a> (and their
  corresponding <a href="#event-handler-event-type" title="event handler event type">event handler
  event types</a>) that must be supported by all <a href="infrastructure.html#html-elements">HTML
  elements</a>, as both content attributes and IDL attributes, and
  on <code><a href="infrastructure.html#document">Document</a></code> and <code><a href="browsers.html#window">Window</a></code> objects, as IDL
  attributes.</p>

  <table><thead><tr><th><a href="#event-handlers" title="event handlers">Event handler</a> </th><th><a href="#event-handler-event-type">Event handler event type</a>
   </th></tr></thead><tbody><tr><td><dfn id="handler-onabort" title="handler-onabort"><code>onabort</code></dfn> </td><td> <code title="event-abort">abort</code>
    </td></tr><tr><td><dfn id="handler-oncanplay" title="handler-oncanplay"><code>oncanplay</code></dfn> </td><td> <code title="event-media-canplay"><a href="the-iframe-element.html#event-media-canplay">canplay</a></code>
    </td></tr><tr><td><dfn id="handler-oncanplaythrough" title="handler-oncanplaythrough"><code>oncanplaythrough</code></dfn> </td><td> <code title="event-media-canplaythrough"><a href="the-iframe-element.html#event-media-canplaythrough">canplaythrough</a></code>
    </td></tr><tr><td><dfn id="handler-onchange" title="handler-onchange"><code>onchange</code></dfn> </td><td> <code title="event-change">change</code> 
    </td></tr><tr><td><dfn id="handler-onclick" title="handler-onclick"><code>onclick</code></dfn> </td><td> <code title="event-click"><a href="infrastructure.html#event-click">click</a></code> 
    </td></tr><tr><td><dfn id="handler-oncontextmenu" title="handler-oncontextmenu"><code>oncontextmenu</code></dfn> </td><td> <code title="event-contextmenu">contextmenu</code> 
    </td></tr><tr><td><dfn id="handler-oncuechange" title="handler-oncuechange"><code>oncuechange</code></dfn> </td><td> <code title="event-cuechange">cuechange</code>
    </td></tr><tr><td><dfn id="handler-ondblclick" title="handler-ondblclick"><code>ondblclick</code></dfn> </td><td> <code title="event-dblclick">dblclick</code> 
    </td></tr><tr><td><dfn id="handler-ondrag" title="handler-ondrag"><code>ondrag</code></dfn> </td><td> <code title="event-drag"><a href="dnd.html#event-drag">drag</a></code>
    </td></tr><tr><td><dfn id="handler-ondragend" title="handler-ondragend"><code>ondragend</code></dfn> </td><td> <code title="event-dragend"><a href="dnd.html#event-dragend">dragend</a></code>
    </td></tr><tr><td><dfn id="handler-ondragenter" title="handler-ondragenter"><code>ondragenter</code></dfn> </td><td> <code title="event-dragenter"><a href="dnd.html#event-dragenter">dragenter</a></code>
    </td></tr><tr><td><dfn id="handler-ondragleave" title="handler-ondragleave"><code>ondragleave</code></dfn> </td><td> <code title="event-dragleave"><a href="dnd.html#event-dragleave">dragleave</a></code>
    </td></tr><tr><td><dfn id="handler-ondragover" title="handler-ondragover"><code>ondragover</code></dfn> </td><td> <code title="event-dragover"><a href="dnd.html#event-dragover">dragover</a></code>
    </td></tr><tr><td><dfn id="handler-ondragstart" title="handler-ondragstart"><code>ondragstart</code></dfn> </td><td> <code title="event-dragstart"><a href="dnd.html#event-dragstart">dragstart</a></code> 
    </td></tr><tr><td><dfn id="handler-ondrop" title="handler-ondrop"><code>ondrop</code></dfn> </td><td> <code title="event-drop"><a href="dnd.html#event-drop">drop</a></code>
    </td></tr><tr><td><dfn id="handler-ondurationchange" title="handler-ondurationchange"><code>ondurationchange</code></dfn> </td><td> <code title="event-media-durationchange"><a href="the-iframe-element.html#event-media-durationchange">durationchange</a></code>
    </td></tr><tr><td><dfn id="handler-onemptied" title="handler-onemptied"><code>onemptied</code></dfn> </td><td> <code title="event-media-emptied"><a href="the-iframe-element.html#event-media-emptied">emptied</a></code>
    </td></tr><tr><td><dfn id="handler-onended" title="handler-onended"><code>onended</code></dfn> </td><td> <code title="event-media-ended"><a href="the-iframe-element.html#event-media-ended">ended</a></code>
    </td></tr><tr><td><dfn id="handler-oninput" title="handler-oninput"><code>oninput</code></dfn> </td><td> <code title="event-input">input</code>
    </td></tr><tr><td><dfn id="handler-oninvalid" title="handler-oninvalid"><code>oninvalid</code></dfn> </td><td> <code title="event-invalid">invalid</code>
    </td></tr><tr><td><dfn id="handler-onkeydown" title="handler-onkeydown"><code>onkeydown</code></dfn> </td><td> <code title="event-keydown">keydown</code> 
    </td></tr><tr><td><dfn id="handler-onkeypress" title="handler-onkeypress"><code>onkeypress</code></dfn> </td><td> <code title="event-keypress">keypress</code> 
    </td></tr><tr><td><dfn id="handler-onkeyup" title="handler-onkeyup"><code>onkeyup</code></dfn> </td><td> <code title="event-keyup">keyup</code> 
    </td></tr><tr><td><dfn id="handler-onloadeddata" title="handler-onloadeddata"><code>onloadeddata</code></dfn> </td><td> <code title="event-media-loadeddata"><a href="the-iframe-element.html#event-media-loadeddata">loadeddata</a></code>
    </td></tr><tr><td><dfn id="handler-onloadedmetadata" title="handler-onloadedmetadata"><code>onloadedmetadata</code></dfn> </td><td> <code title="event-media-loadedmetadata"><a href="the-iframe-element.html#event-media-loadedmetadata">loadedmetadata</a></code>
    </td></tr><tr><td><dfn id="handler-onloadstart" title="handler-onloadstart"><code>onloadstart</code></dfn> </td><td> <code title="event-media-loadstart"><a href="the-iframe-element.html#event-media-loadstart">loadstart</a></code>
    </td></tr><tr><td><dfn id="handler-onmousedown" title="handler-onmousedown"><code>onmousedown</code></dfn> </td><td> <code title="event-mousedown">mousedown</code> 
    </td></tr><tr><td><dfn id="handler-onmousemove" title="handler-onmousemove"><code>onmousemove</code></dfn> </td><td> <code title="event-mousemove">mousemove</code> 
    </td></tr><tr><td><dfn id="handler-onmouseout" title="handler-onmouseout"><code>onmouseout</code></dfn> </td><td> <code title="event-mouseout">mouseout</code> 
    </td></tr><tr><td><dfn id="handler-onmouseover" title="handler-onmouseover"><code>onmouseover</code></dfn> </td><td> <code title="event-mouseover">mouseover</code> 
    </td></tr><tr><td><dfn id="handler-onmouseup" title="handler-onmouseup"><code>onmouseup</code></dfn> </td><td> <code title="event-mouseup">mouseup</code> 
    </td></tr><tr><td><dfn id="handler-onmousewheel" title="handler-onmousewheel"><code>onmousewheel</code></dfn> </td><td> <code title="event-mousewheel">mousewheel</code> 
    </td></tr><tr><td><dfn id="handler-onpause" title="handler-onpause"><code>onpause</code></dfn> </td><td> <code title="event-media-pause"><a href="the-iframe-element.html#event-media-pause">pause</a></code>
    </td></tr><tr><td><dfn id="handler-onplay" title="handler-onplay"><code>onplay</code></dfn> </td><td> <code title="event-media-play"><a href="the-iframe-element.html#event-media-play">play</a></code>
    </td></tr><tr><td><dfn id="handler-onplaying" title="handler-onplaying"><code>onplaying</code></dfn> </td><td> <code title="event-media-playing"><a href="the-iframe-element.html#event-media-playing">playing</a></code>
    </td></tr><tr><td><dfn id="handler-onprogress" title="handler-onprogress"><code>onprogress</code></dfn> </td><td> <code title="event-media-progress"><a href="the-iframe-element.html#event-media-progress">progress</a></code>
    </td></tr><tr><td><dfn id="handler-onratechange" title="handler-onratechange"><code>onratechange</code></dfn> </td><td> <code title="event-media-ratechange"><a href="the-iframe-element.html#event-media-ratechange">ratechange</a></code>
    </td></tr><tr><td><dfn id="handler-onreadystatechange" title="handler-onreadystatechange"><code>onreadystatechange</code></dfn> </td><td> <code title="event-readystatechange"><a href="dom.html#event-readystatechange">readystatechange</a></code>
    </td></tr><tr><td><dfn id="handler-onreset" title="handler-onreset"><code>onreset</code></dfn> </td><td> <code title="event-reset">reset</code>
    </td></tr><tr><td><dfn id="handler-onseeked" title="handler-onseeked"><code>onseeked</code></dfn> </td><td> <code title="event-media-seeked"><a href="the-iframe-element.html#event-media-seeked">seeked</a></code>
    </td></tr><tr><td><dfn id="handler-onseeking" title="handler-onseeking"><code>onseeking</code></dfn> </td><td> <code title="event-media-seeking"><a href="the-iframe-element.html#event-media-seeking">seeking</a></code>
    </td></tr><tr><td><dfn id="handler-onselect" title="handler-onselect"><code>onselect</code></dfn> </td><td> <code title="event-select">select</code>  <!-- [CSSOM] -->
    </td></tr><tr><td><dfn id="handler-onshow" title="handler-onshow"><code>onshow</code></dfn> </td><td> <code title="event-show">show</code>
    </td></tr><tr><td><dfn id="handler-onstalled" title="handler-onstalled"><code>onstalled</code></dfn> </td><td> <code title="event-media-stalled"><a href="the-iframe-element.html#event-media-stalled">stalled</a></code>
    </td></tr><tr><td><dfn id="handler-onsubmit" title="handler-onsubmit"><code>onsubmit</code></dfn> </td><td> <code title="event-submit">submit</code> 
    </td></tr><tr><td><dfn id="handler-onsuspend" title="handler-onsuspend"><code>onsuspend</code></dfn> </td><td> <code title="event-media-suspend"><a href="the-iframe-element.html#event-media-suspend">suspend</a></code>
    </td></tr><tr><td><dfn id="handler-ontimeupdate" title="handler-ontimeupdate"><code>ontimeupdate</code></dfn> </td><td> <code title="event-media-timeupdate"><a href="the-iframe-element.html#event-media-timeupdate">timeupdate</a></code>
    </td></tr><tr><td><dfn id="handler-onvolumechange" title="handler-onvolumechange"><code>onvolumechange</code></dfn> </td><td> <code title="event-media-volumechange"><a href="the-iframe-element.html#event-media-volumechange">volumechange</a></code>
    </td></tr><tr><td><dfn id="handler-onwaiting" title="handler-onwaiting"><code>onwaiting</code></dfn> </td><td> <code title="event-media-waiting"><a href="the-iframe-element.html#event-media-waiting">waiting</a></code>

 
 
 
 
  </td></tr></tbody></table><hr><p>The following are the <a href="#event-handlers">event handlers</a> (and their
  corresponding <a href="#event-handler-event-type" title="event handler event type">event handler
  event types</a>) that must be supported by all <a href="infrastructure.html#html-elements">HTML
  elements</a> other than <code><a href="sections.html#the-body-element">body</a></code>, as both content
  attributes and IDL attributes, and on <code><a href="infrastructure.html#document">Document</a></code> objects,
  as IDL attributes:</p>

  <table><thead><tr><th><a href="#event-handlers" title="event handlers">Event handler</a> </th><th><a href="#event-handler-event-type">Event handler event type</a>
   </th></tr></thead><tbody><tr><td><dfn id="handler-onblur" title="handler-onblur"><code>onblur</code></dfn> </td><td> <code title="event-blur">blur</code> 
    </td></tr><tr><td><dfn id="handler-onerror" title="handler-onerror"><code>onerror</code></dfn> </td><td> <code title="event-error">error</code>
    </td></tr><tr><td><dfn id="handler-onfocus" title="handler-onfocus"><code>onfocus</code></dfn> </td><td> <code title="event-focus">focus</code> 
    </td></tr><tr><td><dfn id="handler-onload" title="handler-onload"><code>onload</code></dfn> </td><td> <code title="event-load">load</code>
    </td></tr><tr><td><dfn id="handler-onscroll" title="handler-onscroll"><code>onscroll</code></dfn> </td><td> <code title="event-scroll">scroll</code>
  </td></tr></tbody></table><hr><p>The following are the <a href="#event-handlers">event handlers</a> (and their
  corresponding <a href="#event-handler-event-type" title="event handler event type">event handler
  event types</a>) that must be supported by <code><a href="browsers.html#window">Window</a></code>
  objects, as IDL attributes on the <code><a href="browsers.html#window">Window</a></code> object, and
  with corresponding content attributes and IDL attributes exposed on
  the <code><a href="sections.html#the-body-element">body</a></code> and <code><a href="obsolete.html#frameset">frameset</a></code> elements:</p>

  <table><thead><tr><th><a href="#event-handlers" title="event handlers">Event handler</a> </th><th><a href="#event-handler-event-type">Event handler event type</a>
   </th></tr></thead><tbody><tr><td><dfn id="handler-window-onafterprint" title="handler-window-onafterprint"><code>onafterprint</code></dfn> </td><td> <code title="event-afterprint">afterprint</code>
    </td></tr><tr><td><dfn id="handler-window-onbeforeprint" title="handler-window-onbeforeprint"><code>onbeforeprint</code></dfn> </td><td> <code title="event-beforeprint">beforeprint</code>
    </td></tr><tr><td><dfn id="handler-window-onbeforeunload" title="handler-window-onbeforeunload"><code>onbeforeunload</code></dfn> </td><td> <code title="event-beforeunload">beforeunload</code>
    </td></tr><tr><td><dfn id="handler-window-onblur" title="handler-window-onblur"><code>onblur</code></dfn> </td><td> <code title="event-blur">blur</code>
    </td></tr><tr><td><dfn id="handler-window-onerror" title="handler-window-onerror"><code>onerror</code></dfn> </td><td> <code title="event-error">error</code>
    </td></tr><tr><td><dfn id="handler-window-onfocus" title="handler-window-onfocus"><code>onfocus</code></dfn> </td><td> <code title="event-focus">focus</code>
    </td></tr><tr><td><dfn id="handler-window-onhashchange" title="handler-window-onhashchange"><code>onhashchange</code></dfn> </td><td> <code title="event-hashchange"><a href="history.html#event-hashchange">hashchange</a></code> 
    </td></tr><tr><td><dfn id="handler-window-onload" title="handler-window-onload"><code>onload</code></dfn> </td><td> <code title="event-load">load</code> 
    </td></tr><tr><td><dfn id="handler-window-onmessage" title="handler-window-onmessage"><code>onmessage</code></dfn> </td><td> <code title="event-message">message</code> 
    </td></tr><tr><td><dfn id="handler-window-onoffline" title="handler-window-onoffline"><code>onoffline</code></dfn> </td><td> <code title="event-offline"><a href="offline.html#event-offline">offline</a></code> 
    </td></tr><tr><td><dfn id="handler-window-ononline" title="handler-window-ononline"><code>ononline</code></dfn> </td><td> <code title="event-online"><a href="offline.html#event-online">online</a></code> 
    </td></tr><tr><td><dfn id="handler-window-onpagehide" title="handler-window-onpagehide"><code>onpagehide</code></dfn> </td><td> <code title="event-pagehide"><a href="history.html#event-pagehide">pagehide</a></code> 
    </td></tr><tr><td><dfn id="handler-window-onpageshow" title="handler-window-onpageshow"><code>onpageshow</code></dfn> </td><td> <code title="event-pageshow"><a href="history.html#event-pageshow">pageshow</a></code> 
    </td></tr><tr><td><dfn id="handler-window-onpopstate" title="handler-window-onpopstate"><code>onpopstate</code></dfn> </td><td> <code title="event-popstate"><a href="history.html#event-popstate">popstate</a></code> 
    </td></tr><tr><td><dfn id="handler-window-onredo" title="handler-window-onredo"><code>onredo</code></dfn> </td><td> <code title="event-redo">redo</code> 
    </td></tr><tr><td><dfn id="handler-window-onresize" title="handler-window-onresize"><code>onresize</code></dfn> </td><td> <code title="event-resize">resize</code>  <!-- [CSSOM] -->
    </td></tr><tr><td><dfn id="handler-window-onscroll" title="handler-window-onscroll"><code>onscroll</code></dfn> </td><td> <code title="event-scroll">scroll</code>
    </td></tr><tr><td><dfn id="handler-window-onstorage" title="handler-window-onstorage"><code>onstorage</code></dfn> </td><td> <code title="event-storage">storage</code> 
    </td></tr><tr><td><dfn id="handler-window-onundo" title="handler-window-onundo"><code>onundo</code></dfn> </td><td> <code title="event-undo">undo</code> 
    </td></tr><tr><td><dfn id="handler-window-onunload" title="handler-window-onunload"><code>onunload</code></dfn> </td><td> <code title="event-unload">unload</code> 
  </td></tr></tbody></table><p class="note">The <code title="handler-window-onerror"><a href="#handler-window-onerror">onerror</a></code>
  handler is also used for <a href="#runtime-script-errors">reporting script errors</a>.</p>

  </div><div class="impl">

  <h5 id="event-firing"><span class="secno">6.1.6.3 </span>Event firing</h5>

  <p>Certain operations and methods are defined as firing events on
  elements. For example, the <code title="dom-click"><a href="editing.html#dom-click">click()</a></code>
  method on the <code><a href="elements.html#htmlelement">HTMLElement</a></code> interface is defined as
  firing a <code title="event-click"><a href="infrastructure.html#event-click">click</a></code> event on the
  element. <a href="references.html#refsDOMEVENTS">[DOMEVENTS]</a></p>

  <p><dfn id="fire-a-simple-event" title="fire a simple event">Firing a simple event named <var title="">e</var></dfn> means that an event with the name <var title="">e</var>, which does not bubble (except where otherwise
  stated) and is not cancelable (except where otherwise stated), and
  which uses the <code><a href="infrastructure.html#event">Event</a></code> interface, must be dispatched at
  the given target.</p>

  <p><dfn id="fire-a-synthetic-mouse-event" title="fire a synthetic mouse event">Firing a synthetic
  mouse event named <var title="">e</var></dfn> means that an event
  with the name <var title="">e</var>, which does not bubble (except
  where otherwise stated) and is not cancelable (except where
  otherwise stated), and which uses the <code><a href="infrastructure.html#mouseevent">MouseEvent</a></code>
  interface, must be dispatched at the given target. The event object
  must have its <code title="">screenX</code>, <code title="">screenY</code>, <code title="">clientX</code>, <code title="">clientY</code>, and <code title="">button</code> attributes
  set to 0, its <code title="">ctrlKey</code>, <code title="">shiftKey</code>, <code title="">altKey</code>, and <code title="">metaKey</code> attributes set according to the current
  state of the key input device, if any (false for any keys that are
  not available), its <code title="">detail</code> attribute set to 1,
  and its <code title="">relatedTarget</code> attribute set to null.
  The <code title="">getModifierState()</code> method on the object
  must return values appropriately describing the state of the key
  input device at the time the event is created.</p>

  <p><dfn id="fire-a-click-event" title="fire a click event">Firing a <code title="event-click">click</code> event</dfn> means <a href="#fire-a-synthetic-mouse-event" title="fire
  a synthetic mouse event">firing a synthetic mouse event named <code title="event-click">click</code></a>, which bubbles and is
  cancelable.</p>

  <p>The default action of these events is to do nothing except where
  otherwise stated.</p>

  </div><div class="impl">

  <h5 id="events-and-the-window-object"><span class="secno">6.1.6.4 </span>Events and the <code><a href="browsers.html#window">Window</a></code> object</h5>

  <p>When an event is dispatched at a DOM node in a
  <code><a href="infrastructure.html#document">Document</a></code> in a <a href="browsers.html#browsing-context">browsing context</a>, if the
  event is not a <code title="event-load">load</code> event, the user
  agent must also dispatch the event to the <code><a href="browsers.html#window">Window</a></code>, as
  follows:</p>

  <ol><li>In the capture phase, the event must propagate to the
   <code><a href="browsers.html#window">Window</a></code> object before propagating to any of the nodes,
   as if the <code><a href="browsers.html#window">Window</a></code> object was the parent of the
   <code><a href="infrastructure.html#document">Document</a></code> in the dispatch chain.</li>

   <li>In the bubble phase, the event must propagate up to the
   <code><a href="browsers.html#window">Window</a></code> object at the end of the phase, unless bubbling
   has been prevented, again as if the <code><a href="browsers.html#window">Window</a></code> object was
   the parent of the <code><a href="infrastructure.html#document">Document</a></code> in the dispatch chain.</li>

  </ol></div><h3 id="atob"><span class="secno">6.2 </span>Base64 utility methods</h3><p>The <code title="dom-windowbase64-atob"><a href="#dom-windowbase64-atob">atob()</a></code> and <code title="dom-windowbase64-btoa"><a href="#dom-windowbase64-btoa">btoa()</a></code> methods allow authors to
  transform content to and from the base64 encoding.</p><pre class="idl">[Supplemental, NoInterfaceObject]
interface <dfn id="windowbase64">WindowBase64</dfn> {
  DOMString <a href="#dom-windowbase64-btoa" title="dom-windowbase64-btoa">btoa</a>(in DOMString btoa);
  DOMString <a href="#dom-windowbase64-atob" title="dom-windowbase64-atob">atob</a>(in DOMString atob);
};
<a href="browsers.html#window">Window</a> implements <a href="#windowbase64">WindowBase64</a>;</pre><p class="note">In these APIs, for mnemonic purposes, the "b" can be
  considered to stand for "binary", and the "a" for "ASCII". In
  practice, though, for primarily historical reasons, both the input
  and output of these functions are Unicode strings.</p><dl class="domintro"><dt><var title="">result</var> = <var title="">window</var> . <code title="dom-windowbase64-btoa"><a href="#dom-windowbase64-btoa">btoa</a></code>( <var title="">data</var> )</dt>

   <dd>

    <p>Takes the input data, in the form of a Unicode string
    containing only characters in the range U+0000 to U+00FF, each
    representing a binary byte with values 0x00 to 0xFF respectively,
    and converts it to its base64 representation, which it returns.</p>

    <p>Throws an <code><a href="common-dom-interfaces.html#invalid_character_err">INVALID_CHARACTER_ERR</a></code> exception if the
    input string contains any out-of-range characters.</p>

   </dd>

   <dt><var title="">result</var> = <var title="">window</var> . <code title="dom-windowbase64-atob"><a href="#dom-windowbase64-atob">atob</a></code>( <var title="">data</var> )</dt>

   <dd>

    <p>Takes the input data, in the form of a Unicode string
    containing base64-encoded binary data, decodes it, and returns a
    string consisting of characters in the range U+0000 to U+00FF,
    each representing a binary byte with values 0x00 to 0xFF
    respectively, corresponding to that binary data.</p>

    <p>Throws an <code><a href="common-dom-interfaces.html#invalid_character_err">INVALID_CHARACTER_ERR</a></code> exception if the
    input string is not valid base64 data.</p>

   </dd>

  </dl><div class="impl">

  <p class="note">The <code><a href="#windowbase64">WindowBase64</a></code> interface adds to the
  <code><a href="browsers.html#window">Window</a></code> interface and the <code>WorkerUtils</code>
  interface (part of Web Workers).</p>

  <p>The <dfn id="dom-windowbase64-btoa" title="dom-windowbase64-btoa"><code>btoa()</code></dfn>
  method must throw an <code><a href="common-dom-interfaces.html#invalid_character_err">INVALID_CHARACTER_ERR</a></code> exception if
  the method's first argument contains any character whose code point
  is greater than U+00FF. Otherwise, the user agent must convert that
  argument to a sequence of octets whose <var title="">n</var>th octet
  is the eight-bit representation of the code point of the <var title="">n</var>th character of the argument, and then must apply
  the base64 algorithm to that sequence of octets, and return the
  result. <a href="references.html#refsRFC4648">[RFC4648]</a></p>
  

  <p>The <dfn id="dom-windowbase64-atob" title="dom-windowbase64-atob"><code>atob()</code></dfn>
  method must run the following steps to parse the string passed in
  the method's first argument:</p>

  <ol><li><p>Let <var title="">input</var> be the string being
   parsed.</p></li>

   <li><p>Let <var title="">position</var> be a pointer into <var title="">input</var>, initially pointing at the start of the
   string.</p></li>

   <li><p>If the length of <var title="">input</var> divides by 4
   leaving no remainder, then: if <var title="">input</var> ends with
   one or two U+003D EQUALS SIGN (=) characters, remove them from <var title="">input</var>.</p></li>

   <li><p>If the length of <var title="">input</var> divides by 4
   leaving a remainder of 1, throw an
   <code><a href="common-dom-interfaces.html#invalid_character_err">INVALID_CHARACTER_ERR</a></code> exception and abort these
   steps.</p>

   </li><li>

    <p>If <var title="">input</var> contains a character that is not
    in the following list of characters and character ranges, throw an
    <code><a href="common-dom-interfaces.html#invalid_character_err">INVALID_CHARACTER_ERR</a></code> exception and abort these
    steps:</p>

    <ul class="brief"><li>U+002B PLUS SIGN (+)
     </li><li>U+002F SOLIDUS (/)
     </li><li>U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9)
     </li><li>U+0041 LATIN CAPITAL LETTER A to U+005A LATIN CAPITAL LETTER Z
     </li><li>U+0061 LATIN SMALL LETTER A to U+007A LATIN SMALL LETTER Z
    </li></ul></li>

   <li><p>Let <var title="">output</var> be a string, initially
   empty.</p></li>

   <li><p>Let <var title="">buffer</var> be a buffer that can have
   bits appended to it, initially empty.</p></li>

   <li>

    <p>While <var title="">position</var> does not point past the end
    of <var title="">input</var>, run these substeps:</p>

    <ol><li>

      <p>Find the character pointed to by <var title="">position</var>
      in the first column of the following table. Let <var title="">n</var> be the number given in the second cell of the
      same row.</p>

      <div id="base64-table">
       <table><thead><tr><th>Character
          </th><th>Number
        </th></tr></thead><tbody><tr><td>A</td><td>0
         </td></tr><tr><td>B</td><td>1
         </td></tr><tr><td>C</td><td>2
         </td></tr><tr><td>D</td><td>3
         </td></tr><tr><td>E</td><td>4
         </td></tr><tr><td>F</td><td>5
         </td></tr><tr><td>G</td><td>6
         </td></tr><tr><td>H</td><td>7
         </td></tr><tr><td>I</td><td>8
         </td></tr><tr><td>J</td><td>9
         </td></tr><tr><td>K</td><td>10
         </td></tr><tr><td>L</td><td>11
         </td></tr><tr><td>M</td><td>12
         </td></tr><tr><td>N</td><td>13
         </td></tr><tr><td>O</td><td>14
         </td></tr><tr><td>P</td><td>15
         </td></tr><tr><td>Q</td><td>16
         </td></tr><tr><td>R</td><td>17
         </td></tr><tr><td>S</td><td>18
         </td></tr><tr><td>T</td><td>19
         </td></tr><tr><td>U</td><td>20
         </td></tr><tr><td>V</td><td>21
         </td></tr><tr><td>W</td><td>22
         </td></tr><tr><td>X</td><td>23
         </td></tr><tr><td>Y</td><td>24
         </td></tr><tr><td>Z</td><td>25
         </td></tr><tr><td>a</td><td>26
         </td></tr><tr><td>b</td><td>27
         </td></tr><tr><td>c</td><td>28
         </td></tr><tr><td>d</td><td>29
         </td></tr><tr><td>e</td><td>30
         </td></tr><tr><td>f</td><td>31
         </td></tr><tr><td>g</td><td>32
         </td></tr><tr><td>h</td><td>33
         </td></tr><tr><td>i</td><td>34
         </td></tr><tr><td>j</td><td>35
         </td></tr><tr><td>k</td><td>36
         </td></tr><tr><td>l</td><td>37
         </td></tr><tr><td>m</td><td>38
         </td></tr><tr><td>n</td><td>39
         </td></tr><tr><td>o</td><td>40
         </td></tr><tr><td>p</td><td>41
         </td></tr><tr><td>q</td><td>42
         </td></tr><tr><td>r</td><td>43
         </td></tr><tr><td>s</td><td>44
         </td></tr><tr><td>t</td><td>45
         </td></tr><tr><td>u</td><td>46
         </td></tr><tr><td>v</td><td>47
         </td></tr><tr><td>w</td><td>48
         </td></tr><tr><td>x</td><td>49
         </td></tr><tr><td>y</td><td>50
         </td></tr><tr><td>z</td><td>51
         </td></tr><tr><td>0</td><td>52
         </td></tr><tr><td>1</td><td>53
         </td></tr><tr><td>2</td><td>54
         </td></tr><tr><td>3</td><td>55
         </td></tr><tr><td>4</td><td>56
         </td></tr><tr><td>5</td><td>57
         </td></tr><tr><td>6</td><td>58
         </td></tr><tr><td>7</td><td>59
         </td></tr><tr><td>8</td><td>60
         </td></tr><tr><td>9</td><td>61
         </td></tr><tr><td>+</td><td>62
         </td></tr><tr><td>/</td><td>63
       </td></tr></tbody></table></div>

     </li>

     <li><p>Append to <var title="">buffer</var> the six bits
     corresponding to <var title="">number</var>, most significant bit
     first.</p></li>

     <li><p>If <var title="">buffer</var> has accumulated 24 bits,
     interpret them as three 8-bit big-endian numbers. Append the
     three characters with code points equal to those numbers to <var title="">output</var>, in the same order, and then empty <var title="">buffer</var>.</p></li>

     <li><p>Advance <var title="">position</var> by one
     character.</p></li>

    </ol></li>

   <li>

    <p>If <var title="">buffer</var> is not empty, it contains either
    12 or 18 bits. If it contains 12 bits, discard the last four and
    interpret the remaining eight as an 8-bit big-endian number. If it
    contains 18 bits, discard the last two and interpret the remaining
    16 as two 8-bit big-endian numbers. Append the one or two
    characters with code points equal to those one or two numbers to
    <var title="">output</var>, in the same order.</p>

    <p class="note">The discarded bits mean that, for instance, <code title="">atob("YQ")</code> and <code title="">atob("YR")</code>
    both return "<code title="">a</code>".</p>

   </li>

   <li><p>Return <var title="">output</var>.</p></li>

  </ol></div><p class="note">Some base64 encoders add newlines or other
  whitespace to their output. The <code title="dom-windowbase64-atob"><a href="#dom-windowbase64-atob">atob()</a></code> method throws an
  exception if its input contains characters other than those
  described by the regular expression bracket expression <code title="">[+/=0-9A-Za-z]</code>, so other characters need to be
  removed before <code title="dom-windowbase64-atob"><a href="#dom-windowbase64-atob">atob()</a></code> is
  used for decoding.</p></body></html>