On 30th of October, Tom Lane committed patch: Implement lookbehind constraints in our regular-expression engine. A lookbehind constraint is like a lookahead constraint in that it consumes no text; but it checks for existence (or nonexistence) of a match *ending* at the current point ...

On 9th of April, Tom Lane committed patch: Support indexing of regular-expression searches in contrib/pg_trgm. This works by extracting trigrams from the given regular expression, in generally the same spirit as the previously-existing support for LIKE searches, though of course the details are far ...