These posts are great for history, but regular expression implementation has moved on considerably from early Thompson implementations whether backtracking or NFAs. There is a considerable body of literature about regex implementation, including many quite convincing implementations and alternate formulations, some of which weren't even done by people at, or from, Bell Labs!<p>We seem to have something of an Eternal September of regex implementation knowledge (abetted by Russ Cox's amazingly selective bibliography in his posts introducing RE2).