XSLT comments

Dear Sir,

As I wanted to use XSLT for the transformation of a XML document, containing
in semantic sense a networkstructure, into a XML document with the same
information but in some treestructure, I established that there is no
instruction to implement an iteration based on a condition (e.g. test the
value of a variable). Wouldn't it be useful to provide such an instruction
in future versions of XSLT?

Yours sincerely

Corneel Theben Tervile