triggering xslt-functions from source

Hi there,

I was wondering if it is possible to trigger xslt-functions out of the
source-tree.

Lets say your source-xml has an element as the following:
<foo function="xsl:tokenize(...)" parameters="..."/>

Is it somehow possible to use that as:
<xsl:value-of select="foo/@function"/>

I know that the above only outputs the value of the function attribute
to the result-tree. But is there a different way to accomplish that?
For example a function that takes a string as a parameter and
evaluates its content as if it was a select statement.

Cheers
Manuel Baehnisch