I agree with Alex that `pu` is not terribly meaningful.  I agree with Keith that when I make union fields more easily accessible, I also usually do it with a field naming macro rather than a dereferencing macro.

That said, I don't see any reason to put `page union` in there.  I'd prefer something like `pg` as a prefix.  If it is important to know it is a union at that location, then leave it explicit as `u.col_fix.recno`.  If we just want a prefix to alleviate collisions, then `pg` is easier to read, to me, than `pu`.