The id global attribute defines a unique 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 author must not use it to convey any information. Particular meaning, for example semantic meaning, must not be derived from the string.
This attribute'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.
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 HTML 5, an ID should start with a letter for compatibility.
| 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 fo 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>. |
| Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
|---|---|---|---|---|---|
| Basic support | (Yes) | (Yes)[1] | (Yes) | (Yes) | (Yes) |
| Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
|---|---|---|---|---|---|---|
| Basic support | (Yes) | (Yes) | (Yes)[1] | (Yes) | (Yes) | (Yes) |
[1] id is a true global attribute only since Gecko 32.0 (Firefox 32.0 / Thunderbird 32.0 / SeaMonkey 2.29).
Element.id that reflects this attribute.
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https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/id