Is it possible to use a lookahead to establish whether one or more characters does/doesn't exist when those characters do not *immediately* follow the lookahead assertion? e.g. Given regex similar to this: ([abc])([def])([ghi]) could I, say, only allow the 'i' in the third group as a match if there was an 'a' in the first group?
It seems to me what you really want is look-behind, not look-ahead. Are you using pcre/perl RE?