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xmlns attribute

Declares a namespace for custom tags in an HTML document.


<element xmlns="" ... >




Property values


A string that specifies the namespace used as a prefix to custom tags, or specifies a URN that uniquely identifies the namespace.

Standards information

There are no standards that apply here.


You can declare multiple namespaces on the html tag, as shown in the following syntax.

<html xmlns:Prefix1 xmlns:Prefix2="">

The syntax for xmlns is based on the W3C XML Namespace Spec. 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.


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.

Code example:

<html xmlns:msie>

    @media all {
       msie\:clientCaps {behavior:url(#default#clientcaps);}
  <body style="background-color: #FFF">
     <msie:clientcaps id="oClientCaps" />
    function window.onload() {
      var bDataBindingAvailable  = false;
      var sDataBindingVersion = '';
      var sDataBindingID =  "{333C7BC4-460F-11D0-BC04-0080C7055A83}"; 
      bDataBindingAvailable = oClientCaps.isComponentInstalled(sDataBindingID,"clsid");
      // if data binding is unavailable, install it:
      if (!bDataBindingAvailable)
        oClientCaps.addComponentRequest(sDataBindingID, "componentid");
        bDataBindingAvailable = oClientCaps.doComponentRequest();


Minimum supported client

Windows XP

Minimum supported server

Windows Server 2003

See also