A regular expression, often abbreviated as a regex, is a sequence of characters that defines a search pattern that can be used to find occurrences ...
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I am and was aware of this. The wording could have been better, maybe "Let's say these are the rules that an email address has to comply with to be a valid one." I just wanted some simple rules to make a regex for, to show the ease and speed that regular expression syntax gives you. This was just an example.