Regexp Result
preg_match("/[A-Z]+/", "123") False
preg_match("/[A-Z][A-Z0-9]+/i", "A123") True
preg_match("/[0-9]?[A-Z]+/", "10GreenBottles") True; matches "0G"
preg_match("/[0-9]?[A-Z0-9]*/i", "10GreenBottles") True
preg_match("/[A-Z]?[A-Z]?[A-Z]*/", "") True; zero or one match, then zero or one match, then zero or more means that an empty string matches
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