Can someone explain Possessive Quantifiers to me? (Regular Expressions)

Question

I am reading the PCRE doc, and it refers to possessive quantifiers, but does not explicitly or specifically define them. I know what a greedy quantifier is, and I

Answer 1

Perhaps the best place to start is Regex Tutorial - Possessive Quantifiers:

When discussing the repetition operators or quantifiers, I explained the difference between greedy and lazy repetition. Greediness and laziness determine the order in which the regex engine tries the possible permutations of the regex pattern. A greedy quantifier will first try to repeat the token as many times as possible, and gradually give up matches as the engine backtracks to find an overall match. A lazy quantifier will first repeat the token as few times as required, and gradually expand the match as the engine backtracks through the regex to find an overall match.

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Possessive quantifiers are a way to prevent the regex engine from trying all permutations. This is primarily useful for performance reasons. You can also use possessive quantifiers to eliminate certain matches.