I have a followup question: How is \G defined in TextMate grammars? I notice from the source code that \G anchors are replaced with a null string if the start of the match isn't equal to `anchor`, but I'm having a hard time following where and why `anchor` is updated during the progress of the parse. How would you describe the meaning of `anchor`? Is it the end of the last match, or something else? Thanks!

On Oct 22, 2012, at 9:11 PM, Corey Johnson &lt;cj(a)github.com&gt; wrote: The regexp is matched aginst a single line, true, but that line will include it’s trailing newline (unless it’s the last line in the document). Stuff wrapped in (?=…), (?!…), (?<=…), and (?<!…) are “look around” asserrions. They will peak at the character after or before the current matching position, but they will not consume the character. So a rule like: { match = 'ba(?=r)'; } will match ‘ba’ when followed by ‘r’, but leave the ‘r’ to be potentially matched by a new rule. Yes, in 1.x \G was undefined, in 2.0 it has a defined behavior, which brings us to Nathan Sobo’s question: It should be the end of the previous match (as you suggest). For a begin/end rule, the end rule’s ‘\G’ will match where the begin rule ended. In the line comment rule we use a negative look-ahead assertion (?!\G) requiring that the end rule is *not* where the begin rule stopped. This is because the begin pattern can match zero characters (it matches optional leading whitespace and does a look-ahead on the two forward slashes, but does not match them), so in the case of no leading whitespace, it will not match any characters. In this case, we do not want the end rule to match immidiately, as that also match zero characters, and we would thus end up with an infinite loop.