HTML attributes are modifiers of HTML elements. They generally appear as name-value pairs, separated by "=", and are written within the start tag of an element, after the element's name:

<tag attribute="value">(content to be modified by the tag)tag>

Where tag names the HTML element, attribute is the name of the attribute, set to the provided value.

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). Leaving attribute values unquoted is considered unsafe.

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 (like the ismap attribute for the img element).

Most elements can take any of several common attributes:

• The id attribute provides a document-wide unique identifier for an element. This can be used by stylesheets to provide presentational properties, by browsers to focus attention on the specific element, or by scripts to alter the contents or presentation of an element. Appended to the URL of the page, it provides a globally unique identifier for an element; typically a sub-section of the page. For example, the ID "Attributes" in http://en.wikipedia.org/wiki/HTML#Attributes
• The class attribute provides a way of classifying similar elements. This can be used for semantic
  Semantics
  Semantics is the study of meaning. It focuses on the relation between signifiers, such as words, phrases, signs and symbols, and what they stand for, their denotata....
  
   or presentation purposes. Semantically, for example, classes are used in microformat
  Microformat
  A microformat is a web-based approach to semantic markup which seeks to re-use existing HTML/XHTML tags to convey metadata and other attributes in web pages and other contexts that support HTML, such as RSS...
  
  s. Presentationally, for example, an HTML document might use the designation class="notation" to indicate that all elements with this class value are subordinate to the main text of the document. Such elements might be gathered together and presented as footnotes on a page instead of appearing in the place where they occur in the HTML source.
• An author may use the style non-attributal codes presentational properties to a particular element. It is considered better practice to use an element’s id or class attributes to select the element with a stylesheet, though sometimes this can be too cumbersome for a simple and specific or ad hoc application of styled properties.
• The title attribute is used to attach subtextual explanation to an element. In most browsers this attribute is displayed as what is often referred to as a tooltip
  Tooltip
  The tooltip or infotip is a common graphical user interface element. It is used in conjunction with a cursor, usually a mouse pointer. The user hovers the cursor over an item, without clicking it, and a tooltip may appear—a small "hover box" with information about the item being hovered...
  
  .

The abbreviation element, abbr, can be used to demonstrate these various attributes:

HTML

This example displays as HTML; in most browsers, pointing the cursor at the abbreviation should display the title text "Hypertext Markup Language."

Most elements also take the language-related attributes lang and dir.

Varieties

HTML attributes are generally classed as required attributes, optional attributes, standard attributes, and event attributes. Usually the required and optional attributes modify specific HTML elements, while the standard attributes can be applied to most HTML elements. Event attributes, added in HTML version 4, allow an element to specify scripts to be run under specific circumstances.

Used by one tag

: , : : , , , , : : , , , : : : : : : , : : , , : , , , , : : : : , : : , , , , :

Used by two tags

and :

• • coords — coordinates of an or a within it.
  • shape — shape of an or a within it. Values: default, rect, circle, poly. and :
  • hreflang — Language code of the linked document.
  • rel — Nature of the linked document (relative to the page currently displayed). Free text for , but uses a set of terms (alternate, appendix, bookmark, chapter, contents, copyright, glossary, help, home, index, next, prev, section, start, stylesheet, subsection).
  • rev — Nature of the currently displayed page (relative to the linked document). Varies for and as for rel. and :
  • archive — archive URL(s)
  • codebase — base URL and :
  • color — text color (deprecated)
  • face — font family (deprecated) and :
  • span — number of columns spanned and :
  • datetime — date and time of text or . and :
  • accept — types of files accepted when uploading or and :
  • frameborder — value (0 or 1) specifies whether to display a border around the or .
  • marginheight — top and bottom margins in pixels around the or .
  • scrolling — value (yes, no, auto) specifies whether to display scroll bars around the or .
  • marginwidth — left and right margins in pixels around the or . and :
  • cols — number of visible columns in or (some variation)
  • rows — number of visible rows in or (some variation) and :
  • usemap — specifies name of a map tag to use with -or- URL of an image-map to use with . and :
  • readonly — specifies read-only text for and . and :
  • media — specifies display device for and . Values: all, aural, braille, handheld, print, projection, screen, tty, tv. and :
  • label — description text for an or . and :
  • abbr — abbreviated version of a table or .
  • axis — category name for a table or .
  • colspan — number of columns spanned by a table or .
  • nowrap — (deprecated) prevents wrapping of a table or .
  • rowspan — number of rows spanned by a table or .
  • scope — no effect on normal browser display, but marks a table or as a logical header for other cells. Values: col, colgroup, row, rowgroup.

Used by multiple tags

• align — , , , , , , , ,

— also (deprecated) in , , to , , , , , , ,

• alt — , , ,
• bgcolor — , , , ,
• border — , ,
• char — , , , , , , ,
• charoff — , , , , , , ,
• charset — , ,
• cite — , , ,
• compact — , , ,
• disabled — , , , , ,
• height - , , , — also (deprecated) ,
• href — , , ,
• hspace — , — also (deprecated)
• longdesc — , ,
• name — , , , , , , , , , , , ,
• size — , , , ,
• src — , , , )
• target — , , , ,
• type — , , , , , , , , ,
• valign — , , , , , , ,
• value — , , , ,
• vspace — , ,
• width — , , , , , , , , , ,

Standard attributes

	id
					dir	lang	xml:lang
					dir	lang	xml:lang
					dir	lang	xml:lang
					dir	lang	xml:lang
				title	dir	lang	xml:lang
	id	class	style	title
	id	class	style	title
	id	class	style	title
	id	class	style	title
	id	class	style	title
	id	class	style	title	dir	lang
	id	class	style	title	dir	lang
	id	class	style	title	dir	lang
	id	class	style	title	dir	lang
	id	class	style	title	dir	lang
	id	class	style	title	dir	lang
	id	class	style	title	dir	lang
	id	class	style	title	dir	lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang
	id	class	style	title	dir	lang	xml:lang	accesskey
	id	class	style	title	dir	lang	xml:lang	accesskey
	id	class	style	title	dir	lang	xml:lang		tabindex
	id	class	style	title	dir	lang	xml:lang		tabindex
	id	class	style	title	dir	lang	xml:lang	accesskey	tabindex
	id	class	style	title	dir	lang	xml:lang	accesskey	tabindex
	id	class	style	title	dir	lang	xml:lang	accesskey	tabindex
	id	class	style	title	dir	lang	xml:lang	accesskey	tabindex
	id	class	style	title	dir	lang	xml:lang	accesskey	tabindex

Event attributes

	onload	onunload
	onload	onunload		onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
			onabort	onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup	onblur	onfocus
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup	onblur	onfocus
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup	onblur	onfocus
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup	onblur	onfocus
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup	onblur	onfocus
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup	onblur	onfocus	onchange
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup	onblur	onfocus	onchange	onselect
				onclick	ondblclick	onmousedown	onmousemove	onmouseout	onmouseover	onmouseup	onkeydown	onkeypress	onkeyup	onblur	onfocus	onchange	onselect