I think the ultimate tool for understanding regexps is Russ Cox's notes: http://swtch.com/~rsc/regexp/ http://swtch.com/~rsc/regexp/ When explained well, the

I think the ultimate tool for understanding regexps is Russ Cox's notes: http://swtch.com/~rsc/regexp/ http://swtch.com/~rsc/regexp/ When explained well, the big picture of NFAs and DFAs is bog simple. I'm sure some of the details are messy, but I expect they rarely matter.