Examples of regex that can cause regex engine to fail
Recursion (php and perl): (?R), (?0) and (?1), (?-1), (?&groupname)
Some people, when confronted with a problem, think "I know, I'll use regular expressions." Now they have two problems. (blog post written by Stack Overflow's founder)*
The only java.lang.String functions that accept regular expressions: matches(s), replaceAll(s,s), replaceFirst(s,s), split(s), split(s,i)
find()): A match may be anywhere in the input string (substrings)
@Wildcard - This page is/should definitely be for comment linking after some introductory, general info. But, I've seen it used inappropriately as a direct duplicate too many times.
@sln A rare example of when you should shoot the messenger.
@sln, I think the correct usage would be to look up the answer to a newly asked regex question in this reference, find the linked Q&A that really does answer the new question and is a dupe, mark the new question as a dupe of that post, and add a comment linking to this page.
I don't understand this treatise. While it is (and has) a functional value and good links, nobody that is a beginner will ever understand anything past the first line. Therefore it is useless as an instructional tool. It's title Reference - What does this regex mean? does not tell you what any particular regex means. It is a mish-mash of links.. an overwhelming blend if you will, of the universe of regex constructs from different engines. To make things worse, some people mark regex questions as a direct duplicate of this question. It's sad ..