Once you have constructed a regular expression, it is evaluated much like an arithmetic expression, that is, it is evaluated from left to right and follows an order of precedence.
From Highest to Lowest, the Order of Precedence of the Regular Expression Operators:
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Operator(s)
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Description
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\
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Escape
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(), (?:), (?=), []
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Parentheses and Brackets
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*, +, ?, {n}, {n,}, {n,m}
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Quantifiers
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^, $, \anymetacharacter
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Anchors and Sequences
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Alternation
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Characters have higher precedence than the alternation operator, which allows 'm|food' to match "m" or "food". To match "mood" or "food", use parentheses to create a subexpression, which results in '(m|f)ood'.
