Question How do I refer back to part of a match in a regular expression - i.e. how do I ask "and the same character of group of characters again"?

Answer Use a back reference.  Capture the part that you might want to repeat in round brackets, the refer back to it later on as \1 - i.e. back reference number 1.

Here's a regular expression that matches a string that ends with the same character that it starts with:

/^(.).*\1$/

Link - Full Worked Example

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