I'm quite certain you meant to write (?!Powered) instead of [^Powered]. The difference is that (?!Powered) asserts that the next bit isn't the string 'Powered' while [^Powered] matches any single character that is not one of 'Pdeorw' (sorted). Your net regex is more like /^X-(P|d|e|o|r|w)/ than anything else (except that using a character class is nicer). Got it?