The tool could be extended to support Unicode, whereas AFAIK it would not be possible to extend it to support backreferences. Are there any other “regex” features that would be impossible to support?
I take back my previous claim, this is a wrong exaggeration.
> The tool could be extended to support Unicode
Not an easy task. There are some things in the standard that do not map neatly to states, notably foldcasing of characters that change the count of characters and the treatment of the generic line boundary. Edit: after browsing UTS#18, I am almost certain that a conforming implementation cannot be mapped as exemplified in the tool. Maybe there's a neat work-around possible.
