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A word boundary, in maximum regex dialects, is a position among w and w (non-word char), or at the start or end of a string if it starts offevolved or ends (respectively) with a word person ([0-9a-za-z_]). Until your regex compiler optimizes options into an o(1) trie shape the way perl’s does, you should in all likelihood be doing a test towards hash membership rather. other regex engines simply aren’t very smart at this. tchrist nov five 'eleven at sixteen:26. For example, recall a totally typically used but extraordinarily problematic normal expression for validating the alias of an e-mail cope with. the normal expression ^[0-9a-z]([-. w]*[0-9a-z])*$ is written to system what's taken into consideration to be a legitimate electronic mail deal with, which includes an alphanumeric man or woman, followed by way of zero or extra characters that may be alphanumeric, periods, or hyphens. A normal expression (once in a while called a rational expression) is a sequence of characters...