My Favorite Question

This is the question I had the most fun answering so far. It's a simple but really effective regex technique that can be used in a surprisingly large number of situations.

Matching or replacing something, except when x, y or z...

Tricks / Answers I had fun with

• Match Any English ASCII Character Including Special Characters
• What's in a $? It depends!
• Matching between Variable Delimiters: Use a Conditional
• One Set of Parentheses, One Group Number: Branch Reset
• At which position in the string did the regex fail?
• Match all possible groups of one to four words
• [][] and friends: So you thought matching brackets was easy?
• Match Partially Duplicated lines
• Refactor a Regex with Subroutines
• Regex for nested (overlapping) matches
• Regex Calculators (RPN and non-RPN)
• Match the last group of (potentially) nested brackets
• Reverse-engineer regex pattern to find number of tokens and length of expected matches
• Replace Match with the Number of the Line where it was Found
• Extract All Unique Lines
• Matching French letters
• Capturing Two Optional Groups that Can Occur in Either Order

Answers I loved reading

• What's a number?
• Replacing accented characters
• Options for Forced Failure (ignore the accepted answer). This is just for fun—the standard is (?!) or (*F) in Perl and PCRE.

Work in progress—I really want to add more here. By far the greatest thrill I get on Stack is when I read an answer that makes me go "Aha!..." and grasp a way of doing things that is so much more efficient than anything I had come up with. I've been blown away quite a few times. And one thing that's for sure is there's no shortage here of people who are a lot brighter than me. :)