Should or should not XML document be transformed by its XSLT PI before it is XIncluded?

Hello! 

Although I searched for "xsl" on this mailing-list archive, I did not received answer to my question: Should or should not XML document be transformed by its XSLT PI before it is XIncluded? I mean simple XSLT PI (usually declared on the second line of XML document). 

Thank You for the answer. Stepan