HTML attribute: Difference between revisions

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Several basic attributes types have been recognized, including: (1) ''required attributes'', needed by a particular element type for that element type to function correctly; (2) ''optional attributes'', used to modify the default functionality of an element type; (3) ''standard attributes'', supported by many element types; and (4) ''event attributes'', used to cause element types to specify scripts to be run under specific circumstances.

Some attribute types function differently when used to modify different element types. For example, the attribute ''name'' is used by several element types, but has slightly different functions in each.<ref name="html4attributes">{{cite web | url=http://www.w3.org/TR/html4/index/attributes.html | title=Index of the HTML 4 Attributes | publisher=W3C | accessdateaccess-date=13 February 2015}}</ref>

==Description==

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<syntaxhighlight lang="html"><element attribute="value">element content</element></syntaxhighlight>

Where <code>element</code> names the HTML element type, and <code>attribute</code> is the name of the attribute, set to the provided <code>value</code>. The value may be enclosed in single or double quotes, although values consisting of certain characters can be left unquoted in HTML (but not XHTML).<ref>{{cite web|url=http://www.w3.org/TR/html401/intro/sgmltut.html#h-3.2.2 |title=On SGML and HTML |publisher=World Wide Web Consortium |access-date=|accessdate=November 16, 2008}}</ref><ref>{{cite web|url=http://www.w3.org/TR/xhtml1/diffs.html#h-4.4|title=XHTML 1.0 - Differences with HTML&#160;4|publisher=World Wide Web Consortium|access-date=|accessdate=November 16, 2008}}</ref> Leaving attribute values unquoted is considered unsafe.<ref>{{cite web|first=Jukka|last=Korpela|url=http://www.cs.tut.fi/~jkorpela/qattr.html|title=Why attribute values should always be quoted in HTML|publisher=Cs.tut.fi |date=July 6, 1998|accessdateaccess-date=November 16, 2008}}</ref>

Although most attributes are provided as paired names and values, some affect the element simply by their presence in the start tag of the element<ref name="tagshtml">{{cite web|url=http://www.w3.org/History/19921103-hypertext/hypertext/WWW/MarkUp/Tags.html |title=Tags used in HTML |publisher=World Wide Web Consortium |date=November 3, 1992 |accessdateaccess-date=November 16, 2008}}</ref> (like the <code>ismap</code> attribute for the <code>img</code> element<ref>{{cite web|url=http://www.w3.org/TR/1999/REC-html401-19991224/struct/objects.html#adef-ismap|title=Objects, Images, and Applets in HTML documents |publisher=World Wide Web Consortium |date=December 24, 1999|accessdateaccess-date=November 16, 2008}}</ref>).

The abbreviation element, <code>abbr</code>, can be used to demonstrate these various attributes:

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==Standard attributes==

''Standard attributes'' are also known as ''global attributes'', and function with a large number of elements.<ref name="globalattribute">{{cite web|url=https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes |title=Global attributes - HTML (HyperText Markup Language) MDN |access-date=|accessdate=2015-02-12}}</ref> They include the basic standard attributes: these include ''accesskey, class, contenteditable, contextmenu, data, dir, hidden, id, lang, style, tabindex, title''. There are also some experimental ones. Both ''xml:lang'' and ''xml:base'' have been deprecated. The multiple ''aria-*'' attributes improve accessibility.<ref name="globalattribute"/> The event handler attributes are listed later on.

Technically all standard attributes must be accepted by all elements, though they will not function with some elements.<ref name="HTMLReference">{{cite web | url=https://developer.mozilla.org/en-US/docs/Web/HTML/Reference | title=HTML reference - HTML (HyperText Markup Language) MDN | accessdateaccess-date=13 February 2015}}</ref> The table below lists some common standard attributes, and some elements they can function with.

{| class="wikitable sortable"