I&#x27;ve used lookbehind assertions (and negative lookbehind assertions) many times.  Most recently I used them to do some complex find&#x2F;replaceing across a pretty large codebase.  My editor supports regex, and I&#x27;m glad it does because it made the job easy.<p><i>From what I see these additions become useful long past the point where using a regex was sensible in the first place.</i><p>Regex stops being a sensible solution when your pattern starts getting overly complex.  The fact that you use one of these features doesn&#x27;t imply your pattern is overly complex.  These are not complex features, they&#x27;re easy to use, and often extremely useful.  For example when straightforward find&#x2F;replace doesn&#x27;t cut it.  What would you suggest, I take 10 minutes to write a Python script for what took me about 15 seconds in my editor&#x27;s Find&#x2F;Replace box?