最常犯的 HTML 標識錯誤 Top 100

 國外的一個網站 W3CLove ，最近對在其網站上進行的 45 萬的網頁驗證進行統計，下面是最頻繁的錯誤和警告列表。

W3CLove是一個用來驗證網頁編寫是否規範的在線網站，不過用它來測試 oschina 頁面的時候，提示錯誤：

Top 100 errors list

1. required attribute "alt" not specified, 1,392,075 times.
2. & did not start a character reference. (& probably should have been escaped as &.), 764,450 times.
3. end tag for "img" omitted, but OMITTAG NO was specified, 663,765 times.
4. end tag for "br" omitted, but OMITTAG NO was specified, 502,366 times.
5. an attribute value specification must be an attribute value literal unless shorttag yes is specified, 463,999 times.
6. an attribute value must be a literal unless it contains only name characters, 337,970 times.
7. required attribute "type" not specified, 293,050 times.
8. document type does not allow element "div" here; missing one of "object", "applet", "map", "iframe", "button", "ins", "del" start-tag, 274,987 times.
9. document type does not allow element "p" here; missing one of "object", "applet", "map", "iframe", "button", "ins", "del" start-tag, 202,423 times.
10. document type does not allow element "li" here; missing one of "ul", "ol", "menu", "dir" start-tag, 196,060 times.
11. an img element must have an alt attribute, except under certain conditions. for details, consult guidance on providing text alternatives for images., 164,988 times.
12. end tag for "input" omitted, but OMITTAG NO was specified, 160,066 times.
13. end tag for "p" omitted, but OMITTAG NO was specified, 142,452 times.
14. end tag for "ul" which is not finished, 142,081 times.
15. end tag for element "a" which is not open, 115,545 times.
16. document type does not allow element "div" here; missing one of "applet", "object", "map", "iframe", "button" start-tag, 115,358 times.
17. end tag for "li" omitted, but OMITTAG NO was specified, 101,451 times.
18. element "div" undefined, 98,741 times.
19. reference to entity "action" for which no system identifier could be generated, 93,877 times.
20. document type does not allow element "link" here, 91,422 times.
21. document type does not allow element "a" here, 84,233 times.
22. reference to entity "id" for which no system identifier could be generated, 82,970 times.
23. document type does not allow element "div" here; missing one of "object", "ins", "del", "map", "button" start-tag, 82,761 times.
24. end tag for element "div" which is not open, 82,144 times.
25. document type does not allow element "input" here; missing one of "p", "h1", "h2", "h3", "h4", "h5", "h6", "div", "pre", "address", "fieldset", "ins", "del" start-tag, 80,011 times.
26. document type does not allow element "li" here; missing one of "ul", "ol" start-tag, 77,854 times.
27. character data is not allowed here, 73,051 times.
28. there is no attribute "width", 72,246 times.
29. attribute property not allowed on element meta at this point., 72,024 times.
30. end tag for "meta" omitted, but OMITTAG NO was specified, 71,601 times.
31. document type does not allow element "style" here, 70,476 times.
32. reference to entity "nbsp" for which no system identifier could be generated, 69,629 times.
33. reference to entity "widgetid" for which no system identifier could be generated, 69,565 times.
34. syntax of attribute value does not conform to declared value, 66,937 times.
35. element meta is missing one or more of the following attributes: http-equiv, itemprop, name., 65,735 times.
36. document type does not allow element "meta" here, 64,134 times.
37. reference to entity "cat" for which no system identifier could be generated, 60,781 times.
38. there is no attribute "height", 60,035 times.
39. end tag for "div" omitted, but OMITTAG NO was specified, 59,892 times.
40. an attribute specification must start with a name or name token, 59,374 times.
41. bad value category tag for attribute rel on element a: keyword category is not registered., 58,762 times.
42. consecutive hyphens did not terminate a comment. -- is not permitted inside a comment, but e.g. - - is., 57,425 times.
43. document type does not allow element "div" here, 56,466 times.
44. reference to entity "widgettype" for which no system identifier could be generated, 54,850 times.
45. document type does not allow element "option" here, 54,802 times.
46. reference to entity "sectionid" for which no system identifier could be generated, 53,532 times.
47. value of attribute "align" cannot be "absmiddle"; must be one of "top", "middle", "bottom", "left", "right", 52,637 times.
48. element "g:plusone" undefined, 50,184 times.
49. end tag for "link" omitted, but OMITTAG NO was specified, 50,006 times.
50. reference to entity "postid" for which no system identifier could be generated, 48,854 times.
51. character "/" is not allowed in the value of attribute "id", 47,406 times.
52. document type does not allow element "script" here, 47,169 times.
53. document type does not allow element "p" here; missing one of "object", "ins", "del", "map", "button" start-tag, 47,167 times.
54. element "br" undefined, 46,530 times.
55. NET-enabling start-tag not immediately followed by null end-tag, 45,105 times.
56. there is no attribute "src", 44,667 times.
57. end tag for element "p" which is not open, 44,416 times.
58. document type does not allow element "tr" here, 44,374 times.
59. there is no attribute "href", 43,999 times.
60. there is no attribute "target", 43,848 times.
61. the width attribute on the td element is obsolete. Use CSS instead., 43,173 times.
62. element "a" undefined, 42,579 times.