Why or how do you want to reverse a regex? as in, when would it be useful?

Also can you give an example of a regex and the xeger? (I really don't see how you want to reverse them... which makes it ofcourse impossible for me, and perhaps otehers too, to come up with a test)

As a side note, but still relevant: the purpose of a back-reference is to say: match X and at a later time in the string match X again. basiclly you could have a string: abcb and a regex m/(b).\1/. Now how can you reverse that? you could try m/\1.(b)/ which obviously makes no sense, since a back reference is only set after a matching-group...

Update: I found some intresting posts on perl.perl5.port (dated end 2001, the sexeger node is dated 2000 so these should be newer). One of the most intresting I seen on this subject is: http://www.nntp.perl.org/group/perl.perl5.porters/47521. I also looked up the full thread (or atleast tried to), links can be found in the readmore.