If you squint and turn your head XML Schema's content models look a lot like primitive regular expressions.

Which, if I understand it correctly, is the approach taken by Relax NG.

A RELAX NG schema specifies a pattern for the structure and content of an XML document. A RELAX NG schema thus identifies a class of XML documents consisting of those documents that match the pattern. http://xml.coverpages.org/relax.html

(caveat: my knowledge of this is limited to light reading)

Check out:

In reply to Re: Re: Re: Abusing Regular Expressions by qq
in thread Abusing Regular Expressions by samtregar

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