Namespace separator

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

The namespace separator (|) separates the selector from the namespace, identifying the namespace, or lack thereof, for a type selector.

/* Links in the namespace named myNameSpace */
myNameSpace|a {
  font-weight: bold;
}
/* paragraphs in any namespace (including no namespace) */
*|p {
  color: darkblue;
}
/* heading level 2 not in a namespace */
|h2 {
  margin-bottom: 0;
}

Type selectors and the universal selector allow an optional namespace component. When a namespace has been previously declared via @namespace, these selectors can be namespaced by prepending the selector with the name of the namespace separated by the namespace separator (|). This is useful when dealing with documents containing multiple namespaces such as HTML with inline SVG or MathML, or XML that mixes multiple vocabularies.

ns|h1 - matches <h1> elements in namespace ns
*|h1 - matches all <h1> elements
|h1 - matches all <h1> elements outside of any declared or implied namespace

Syntax

namespace|element { style properties }

Examples

By default, all elements in an HTML or SVG element have a namespace as the http://www.w3.org/1999/xhtml and http://www.w3.org/2000/svg namespace are implied. The document.createElementNS method, with an empty string for the namespace parameter, can be used to create elements with no namespace.

Named namespace example

In this example, all elements are in a namespace.

HTML

No namespaces are explicitly declared in the HTML or within the SVG.

<p>This paragraph <a href="#">has a link</a>.</p>

<svg width="400" viewBox="0 0 400 20">
  <a href="#">
    <text x="0" y="15">Link created in SVG</text>
  </a>
</svg>

CSS

The CSS declares two namespaces, then assigns styles to links globally (a), to links in no namespace (|a), to links in any namespace or no namespace (*|a), and then to two different named namespaces (svgNamespace|a and htmlNameSpace|a).

@namespace svgNamespace url("http://www.w3.org/2000/svg");
@namespace htmlNameSpace url("http://www.w3.org/1999/xhtml");
/* All `<a>`s in the default namespace, in this case, all `<a>`s */
a {
  font-size: 1.4rem;
}
/* no namespace */
|a {
  text-decoration: wavy overline lime;
  font-weight: bold;
}
/* all namespaces (including no namespace) */
*|a {
  color: red;
  fill: red;
  font-style: italic;
}
/* only the svgNamespace namespace, which is <svg> content */
svgNamespace|a {
  color: green;
  fill: green;
}
/* The htmlNameSpace namespace, which is the HTML document */
htmlNameSpace|a {
  text-decoration-line: line-through;
}

Result

The selector |a, a link not in a namespace, doesn't match any links. In HTML, the http://www.w3.org/1999/xhtml is implied, meaning all HTML is in a namespace, even if none is explicitly declared. In SVG, even if not explicitly set, the http://www.w3.org/2000/svg namespace is also implied. This means all the content is within at least one namespace.

Default namespace and no namespace

In this example, we use JavaScript to create an element without a namespace and append it to the document. We set the SVG namespace to be the default namespace by defining the unnamed namespace with @namespace.

Note: If a default, or unnamed, namespace is defined, universal and type selectors apply only to elements in that namespace.

HTML

No namespaces are explicitly declared in the HTML or within the SVG.

<p><a href="#">A link</a> in the implied HTML namespace.</p>

<svg width="400" viewBox="0 0 400 20">
  <a href="#">
    <text x="0" y="15">Link created in SVG namespace</text>
  </a>
</svg>

JavaScript

With JavaScript, with document.createElementNS, we create an anchor link without a namespace, then append the link.

// create 'no namespace' anchor
const a = document.createElementNS("", "a");
a.href = "#";
a.appendChild(document.createTextNode("Link created without a namespace"));

document.body.appendChild(a);

CSS

We declare a namespace with @namespace. By omitting the name for the namespace, the @namespace declaration creates a default namespace.

/* By omitting a name, this sets SVG as the default namespace */
@namespace url("http://www.w3.org/2000/svg");

/* `<a>` in the default (set to SVG) namespace */
a {
  font-size: 1.4rem;
}

/* `<svg>` and `<p>` in the default (set to SVG) namespace */
svg,
p {
  border: 5px solid gold;
}

/* links outside of any namespace */
|a {
  text-decoration: wavy underline purple;
  font-weight: bold;
}

/* links with any namespace or no namespace */
*|a {
  font-style: italic;
  color: magenta;
  fill: magenta;
}

Result

The selector with no namespace separator, the a, matched only the SVG <a> elements, as SVG was set as the default namespace.

The selector with no namespace, the |a, matched the JavaScript defined and appended <a>, as that node is the only node that doesn't have a default namespace.

Specifications

Specification
CSS Namespaces Module Level 3 # declaration

Browser compatibility

	Desktop					Mobile
	Chrome	Edge	Firefox	Opera	Safari	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet	WebView Android
`Namespace_separator`	1	12	1	8	3	18	4	14	1	1.0	37

Syntax

Examples

Named namespace example

HTML

CSS

Result

Default namespace and no namespace

HTML

JavaScript

CSS

Result

Specifications

Browser compatibility

See also