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id (attribute)

The id global attribute defines an identifier (ID) which must be unique in the whole document. Its purpose is to identify the element when linking (using a fragment identifier), scripting, or styling (with CSS).

This attribute's value is an opaque string: this means that web authors should not rely on it to convey human-readable information (although having your IDs somewhat human-readable can be useful for code comprehension, e.g. consider ticket-18659 versus r45tgfe-freds&[email protected]).

id's value must not contain whitespace (spaces, tabs etc.). Browsers treat non-conforming IDs that contain whitespace as if the whitespace is part of the ID. In contrast to the class attribute, which allows space-separated values, elements can only have one single ID value.

Note: Using characters except ASCII letters, digits, '_', '-' and '.' may cause compatibility problems, as they weren't allowed in HTML 4. Though this restriction has been lifted in HTML5, an ID should start with a letter for compatibility.

Specifications

Specification Status Comment
HTML Living Standard
The definition of 'id' in that specification.
Living Standard No change from latest snapshot, HTML 5.1
HTML 5.1
The definition of 'id' in that specification.
Recommendation Snapshot of HTML Living Standard, no change from HTML5
HTML5
The definition of 'id' in that specification.
Recommendation Snapshot of HTML Living Standard, now accept '_', '-' and '.' if not at the beginning of the id. It is also a true global attribute.
HTML 4.01 Specification
The definition of 'id' in that specification.
Recommendation Supported on all elements but <base>, <head>, <html>, <meta>, <script>, <style>, and <title>.

Browser compatibilityUpdate compatibility data on GitHub

Desktop
Chrome Edge Firefox Internet Explorer Opera Safari
id Yes 12 32
32
? — 32
id is a true global attribute only since Firefox 32.
Yes Yes Yes
Mobile
Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet
id Yes Yes 32
32
? — 32
id is a true global attribute only since Firefox 32.
Yes Yes Yes

See also

© 2005–2020 Mozilla and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/id