"...
So you need to write a single pattern that matches either of two different patterns (the "or" case) or both of two patterns (the "and" case) or that reverses the sense of the match ("not").
This situation arises often in configuration files, web forms, or command-line arguments.
..."

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...It's not a pretty picture, and in a regular program, you'd almost never do this"...

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"...this very place is the Land of Lotuses..." / Hakuin Ekaku Zenji