I apologize for giving less consideration to your solution than to
David's, just because I didn't grasp that they were almost the same.

And sorry for not clearly separating what I am trying to do from what
your and David's approaches were. You wrote:

Now you've got me even more confused.

What I said was that my approach did *not* use a stylesheet to generate a stylesheet.

Neither does David's.

Of course not, you are absolutely right. The confusion was introduced by
me, I suppose, after having read how you think of your solution:

This is a "meta-stylesheet" kind of application, but not in the sense
that it's a stylesheet that generates a stylesheet, but rather only
in the sense that its traversal logic is internally configurable rather than being done in the usual way, by traversing the input.