Helen,

H> 1) the semantics were identical whether the search criteria were in the ON
H> clause or the WHERE clause

I have always thought that the criteria in the "on" clause are applied
on the table to be joined, while the criteria in the "where" clause
are applied to the resulting set.

H> 2) it's not good practice to merge search conditions with join conditions

First, one could ask why would it be bad practice if the semantics are
identical, then I tend to skip recommendations along the lines of
"it's not good to..." without a bit of convincing explanation. But
that's just me. :-)

H> I'd also like to know at what point the semantics changed. Was this a Fb
H> 1.5 thing, or was it already done by the time we had Fb 1.0?

I might have an old IB5.6 around if you need me to perform a test.
Although I'd expect it to work like the latest Firebird.

Ciao
--
Nando Dessena
http://www.flamerobin.org