I don't think we need to preserve absolutely all the existing behavior
to the letter. We do need to preserve the behavior for sensible cases
that people might be reasonably be using currently; and if there's
anything somewhat obscure but really useful that you currently get by
using some clever trick, them we should provide some reasonable way to
get that functionality with the new stuff too. But this doesn't mean
all existing code must continue to behave in exactly the same way.
--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services