See also: How to search for whole words?
For my purposes, I find that the Discourse search engine works well but its limitations are well known. It doesn’t purport to be a fantastic, all-singing all-dancing, search engine. (That is a pity because only searching in local, structured content opens up a lot more possibilities than a general search engine that operates across the text of the whole public web.)
Bottom line: It’s open source so y’all feel free to submit a patch that adds more advanced search functionality. 
Also, as I wrote last time:
A forum would only enable regex functionality for users with consideration and care because an accidental or malicious regex could chew up lots of server-side CPU but without achieving much or anything at all.
(The regex may have been supplied explicitly by the more advanced user or implicitly from the functionality offered by the search function.)
