XML/DOM sorting

[mrkkhattak]

<root>
	<entity name="Khattak" />
	<state>
		<working>yes</working>
	</state>
	<db>
		<user>userName</user>
		<password></password>
	</db>
</root>

I want to sort it alphabetically as the following using simpleXML or DOM in PHP.

<root>
	<db>
		<password></password>	
		<user>userName</user>
	</db>
	<entity name="Khattak" />
	<state>
		<working>yes</working>
	</state>
</root>

Thanks in advance.