"Rui Martins" <Rui.Martins@PDMFC.com> writes:
> My reasoning is:
> Why would the exact same sub-expression, return different results when
> either preceded or followed by something.
It *isn't* returning different results; you are testing for different
things in these two cases, namely whether there is a match to the whole
pattern or just a parenthesized subpattern. In none of these examples
was there any match to '(something)' --- there couldn't possibly be,
because "something" isn't in the data string.
regards, tom lane
