regular expression matching in <assert>

Are matches() and tokenize() supported inside <assert> when doing schema validation?  I am applying an assertion to an element with a 'target' attribute whose value is "s1 s2", yet the following assertion is failing:

<xsd:assert test="if (matches(@target, '.*')) then true()  else false()"  xpathDefaultNamespace="##targetNamespace"/>

Any guidance would be appreciated.

Thanks,
Jim