Add source and verification to each regular expression using grep

[odomojuli]

Came across some regular expression variants in this twitter thread from 2020:
https://twitter.com/avicoder/status/1267857981925765120

Regular expressions may vary in usage but I would like to verify some samples against grep.
Not entirely sure I want to be pointing to existing codebases with real examples, since I find that in poor taste.
Would appreciate suggestions for posting verification of regular expressions.

A number of competing repositories either have invalid or deprecated expressions, this an informal attempt to at least update these sources in one place.