Re: Namespaces conventions: Why ALWAYS "http:..." tags

There is useful information about XML Namespaces at:
http://www.rpbourret.com/xml/NamespacesFAQ.htm

Whenever I looked into XSLT stylesheets with namespace declarations I see
ALWAYS a scheme like

xmlns:xsl="http://www.w3.org/1999/XSL/Transform"

or more general

xmlns:foo="http://www.somedomain.com/foobarlabel"

This is somehow confusing because the namespace has nothing to do with a WWW Hyperlinks/URLs.
From my point fo view it is just a tag or label which could be named

xmlns:foo="aabbccdd"

as well
Or is there somewhere a specs which requires a "http...." declaration

What is the reason why all the coders use "http...." URL like namespace names ?

Ben

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Regards,
Mukul Gandhi