XSLT Design

This should be for single transformation using a XML file with XSLT 1 or 2
to produce a PDF file.

Design Patterns :

Are there specific design patterns or ideas on how to structure XSLT code
such as to make them more readable and maintainable. This can be a problem
since both the formatting code and logic code can get intertwined in the
file and can get messy if somebody is continuously making changes on top of
it.

Design documents :

Are there any standard templates for writiing External design document and
internal design document  for XSLT. The idea is to write whatever is being
read from the XML such as its understandable to a layman.


Any suggestions or tips are welcome.

Sajeesh