REGEX

Learning Resources

RegexOne - Learn Regular Expressions - Lesson 1: An Introduction, and the ABCsRegexOne - Learn regular expressions with simple, interactive exercises.

GitHub - ziishaned/learn-regex: Learn regex the easy wayGitHub

Filter Bypass

I'd say that mastering regular expressions could be enough to come up with bypasses.

https://security.stackexchange.com/questions/71169/xss-bypass-this-regexpsecurity.stackexchange.com