The big problem with regexes is debugging them, in the rare case when you don't nail them on the first go.
Fortunately Emacs includes a little tool that helps with this: regexbuilder. You can run regexbuilder with the following command:
M-x re-builder
This little handy thing creates highlights all matches to the regex, that you are currently writing, in the other visible buffers. Extremely useful!
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