CSSNamespaceRule

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since ⁨April 2017⁩.

TheCSSNamespaceRule interface describes an object representing a single CSS@namespaceat-rule.

Instance properties

Inherits properties from its ancestorCSSRule.

CSSNamespaceRule.namespaceURI: Returns a string containing the text of the URI of the given namespace.
CSSNamespaceRule.prefix: Returns a string with the name of the prefix associated to this namespace. If there is no such prefix, returns an empty string.

Inherits methods from its ancestorCSSRule.

The stylesheet includes a namespace as the only rule. Therefore the firstCSSRule returned will be aCSSNamespaceRule.

css

@namespace url("http://www.w3.org/1999/xhtml");

const myRules = document.styleSheets[0].cssRules;console.log(myRules[0]); // A CSSNamespaceRule

Specification
CSS Object Model (CSSOM) # the-cssnamespacerule-interface

This page was last modified on⁨Nov 7, 2025⁩ byMDN contributors.