Next: Regular Expression Functions, Up: Searching and Replacing [Index]
Emacs’s regexp engine is nowhere near as user-friendly as it could be. It’s old, weathered and too entrenched — and heavily modified to suit Emacs’s peculiar needs — to be easily replaced. In practical terms, that causes confusion in regexp building for people unaccustomed to Emacs’s quirky regexp engine. It’s even worse if you write elisp as you have to escape the escape character as Emacs’s C-style string reader would otherwise trigger on backslashes.
I will not cover regular expressions in great detail since that is a whole book onto itself. Instead, I will tell you how Emacs’s regexp engine differs from modern ones.