regex101.com has a convenient searchable cheat sheet for all the somewhat odd but powerful functions like negative lookbehind/lookahead with a brief explanation of each, a regex pattern input with checkable boxes that helps you get down single replacements vs global replacements, a large input that lets you dump text to test against the pattern, an explanation on the right of what each symbol is trying to match, and the left side lets you switch between the different flavors to see some of the variants between languages/standards. I still have a lot to learn before I’ll consider it mastered, but I have enough common stuff memorized now that it works great for me!