Hello, I am trying to use semantic actions in Boost.Xpressive, and I have a couple of questions: 1. When a semantic action is attached to a subexpression of a regex, what is the meaning of _, s1, s2 etc. in the semantic action? For example, suppose you have the following regex: ((s1 = xpr1)[action]) >> (s2 = xpr2) Inside 'action': - is it valid to use '_'? - if so does it refer to just the portion matched by xpr1? - is it valid to use 's1'? - is it valid to use 's2'? 2. Is there a way to access the regex_id of the regex to which a semantic action belongs from the semantic action? More generally, can a semantic action be written as a custom function object that takes as argument some sort of environment (perhaps a match_results<>)? Thanks, Nate