The note in prefixDef begins, "Where matchPattern and replacementPattern are both supplied." But aren't both required?
<prefixDef> can have text content only, if the user prefers a prose description instead of an explicit replacement operation.
John is right. att.patternReplacement says both attributes are mandatory.
Ah -- I think I ended up making them mandatory because they'd been mandatory on <cRefPattern> in the past. Curses. Have to think about that.
I've removed that clause in rev 11581. Thanks John. Closing the ticket.