In confg.sgml, in the section about max_stack_depth, there's this sentence:
"The safety margin is needed because the stack depth is not checked in
every routine in the server, but only in key potentially-recursive
routines such as expression evaluation."
Since the change in expression evaluation in v10, there's probably a
better example of recursive routines, but I'm not sure what that would
be.
-John Naylor