Documentation for regex operator

Hi,

I didn't see a placeholder in the spec for this, so
thought I'd mention it: the regex operator =~ is
not documented anywhere, just used in the example
in 11.2.1.6 and mentioned in the table listing all
operators.

The feature is probably familiar to all of you, but
its less so for users coming from an SQL background
who will be looking for the equivalent to the LIKE
operator. As such I think it's worth documenting more
fully.

Apologies if this is already on the TODO list.

Cheers,

L.