$bbs_text = preg_replace("/([htf]{1,2}tp[s]?:\/\/[[:alnum:]-_]{3,}.[[:alnum:][:punct:]]{3,})([[:space:]\n".chr(0xa1)."-".chr(0xff)."])/Ui","[url=\\1]\\1[/url]\\2", $bbs_text);

请教大家谁能详细的解释一下，尤其是([[:space:]\n".chr(0xa1)."-".chr(0xff)."])/Ui这段，请高手不论赐教！谢谢