xmlns (HTML attribute)

Depr. Version
No XHTML 1.0
Browser support (more…)
IE7 FF1+ SA3+ OP9.2+
None Full Full Full


xmlns="namespace URI"


Here the xmlns attribute is used to define the default namespace of an XHTML document:

<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">


The xmlns attribute on its own is used to declare the default namespace URI for a document, which in an XHTML document will always have the value "http://www.w3.org/1999/xhtml". However this attribute is rather special in XML terms, because it’s also used as a prefix to define additional namespaces for a document. For example, the attribute xmlns:dc would declare a namespace URI for elements with the prefix dc (Dublin Core).


The value of this attribute must be a fully-qualified URI (local paths and empty strings are not permitted). The URI will not be resolved when the document is parsed, and in fact it doesn’t need to point to an actual resource at all; the use of URIs is simply to ensure that namespaces are predictably unique to their creator.


Internet Explorer Firefox Safari Opera
5.5 6.0 7.0 1.0 1.5 2.0 1.3 2.0 3.0 9.2 9.5
None None None Full Full Full None None Full Full Full

Since namespaces are an XML construct, it’s only reasonable to judge their behavior for HTML in terms of XHTML documents served as XML; therefore Internet Explorer, Safari 1.3 and Safari 2 must be considered to have no support for this attribute, because they don’t support true XHTML. Over and above that, the compatibility information shows which browsers recognise the xmlns attribute as referring to the default namespace.

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