Thank you for the links to the various tutorials and discussions. I have read all those over the many years I have used regexes. I feel fairly confident using regexes, including lookarounds, although the dynamic types are still fairly new to me. I am looking for something a little more abstract and theoretical that would probably get into NFA and DFA. I have read the section in Mastering Regular Expressions towards the end that introduces the concepts, but would like more info.