XMLNS Attribute

Internet Development Index

Declares a namespace for custom tags in an HTML document.


HTML <HTML XMLNS:sNamespace ... >

Possible Values

sNamespaceString that specifies the namespace used as a prefix to custom tags or a Uniform Resource Name (URN) that uniquely identifies the namespace.


The syntax for XMLNS is based on the W3C XML Namespace Spec Non-Microsoft link. Although the World Wide Web Consortium (W3C) document allows you to declare namespaces on all tags, Microsoft® Internet Explorer 5 supports namespace declaration only on the html tag.

You can declare multiple namespaces on the html tag, as the syntax below shows:

<HTML XMLNS:Prefix1 XMLNS:Prefix2="www.microsoft.com">


This example shows how to declare a namespace when one of the default behaviors in Internet Explorer, clientCaps, is used as a custom tag in an HTML document. Note that the declared namespace (in this case, MSIE) is a prefix to the name of the default behavior in the custom tag. This example also shows how the clientCaps behavior can be used to install the Internet Explorer Data Binding component, if the component does not already exist in the user's system.

@media all {
MSIE\:clientCaps {behavior:url(#default#clientcaps);}
function window.onload()
var bDataBindingAvailable  = false;
var sDataBindingVersion = '';
var sDataBindingID =
bDataBindingAvailable =
// if data binding is unavailable, install it
if (!bDataBindingAvailable)
oClientCaps.addComponentRequest (sDataBindingID,
bDataBindingAvailable = oClientCaps.doComponentRequest();
<MSIE:CLIENTCAPS ID="oClientCaps" />
This feature requires Microsoft® Internet Explorer 5 or later. Click the following icon to install the latest version. Then reload this page to view the sample.

Standards Information

There is no public standard that applies to this attribute.

Applies To