Generating XProc/XSL with XProc/XSL

Let’s say I want to write some XSL templates that allow me to map arbitrary XML grammars into SVG.  I know what I want the SVG to look like, and I know that the intended XML grammar is guaranteed to have certain pieces of data that I want to map to SVG using XSL.  

I’ve been in similar situations many times, but even with Oxygen (and I love Oxygen to bits—it’s a fantastic IDE!) it can get tedious. 

I have occasionally stumbled into the DocBook XSL files and seen comments stating “This is a generated XSL file—do not edit!”

…

How does one go about writing XProc or XSL to generate XSL?  I mean, how do you do it intelligently?  I’m looking for:

human-friendly method of writing the “generator” code
human-friendly code produced by the “generator”
flexible, modular code produced by the “generator”

—Zearin (Tony)