[Patch] Regex comments

[Jonathan Wakely]

+  // This function serves in different modes, DFS mode or BFS mode, indicated
+  // by template variable __dfs_mode. See _M_main for details.

I think this would make more sense if you replace "serves" with
"operates", and __dfs_mode is a template parameter, not a variable.

+  // It applys a Depth-First-Search (aka backtracking) on given NFA and input
+  // string.

s/applys/applies/

+  // At the very beginning the executor stands in the start state, then it try

s/try/tries/

+  // It first computes epsilon clousure for every state that's still matching,

s/clousure/closure/

+  // The order of which states needs to be recursively applied DFS matters,
+  // depend on which greedy mode we use.

I don't understand this sentence at all, sorry.  Can you explain it in
other terms, and I'll try to suggest better phrasing?

+  // It significantly reduces potential duplicate states, so have a better
+  // upper bound; but it deserves more overhead.

s/have/has/

And should it say "requires" not "deserves"?

+      else // Ungreedy mode

s/Ungreedy/non-greedy/

+          // DON't attempt anything, because there's already someone

s/DON't/DON'T/
someone?  Should it be "something" or "another state" instead?

+              // has one more time ungreedy quantifier loop.

???
Maybe "requires another iteration of a non-greedy quantifier loop" ?

+      // This prevents the executor from get into infinite loop when use

This should be "... getting into an infinite loop when using ..."