>> Only functions that call FooBar() change. That's exactly the same as
xslt.

Yes, but in C, calls to functions are explicit; in XSLT, calls to
templates are implicit.  That makes all the difference.

>> If you (re) define the template that matches FooBar then the
processing of FooBar elements changes That's not Fragile, it's how it's
expected to be, surely.

Yes, if a child takes a gun and shoots himself in the foot, you can say
"that's to be expected." Me, I say "let's build in a safety catch."  :)

-Mike