[1wd]

There are many differencese between "compatible" regular expressions, for (many) examples read the end of section "Important Notes About Lookbehind" on [1] or compare 24 dialects on [2] for example.

[1] http://www.regular-expressions.info/lookaround.html [2] http://www.regular-expressions.info/refadv.html

[macintux]

Erlang requires doubling up on escape backslashes, which generally causes me grief even after I flail about and finally remember it. Subtleties abound.

[pjtr]

Another strange one is the (old) Visual Studio syntax with its :i (actually often quite helpful) and $1 instead of \1 (even in the new syntax).

https://msdn.microsoft.com/en-us/library/2k3te2cs(v=vs.110)....