Fix substr

Ps:
          string strip_tags ( string $str [, string $allowable_tags ] )
*This function tries to return a string with all NULL bytes, HTML and PHP tags stripped from a given str. It uses the same tag stripping state machine as the fgetss() function.*
see http://php.net/manual/en/function.strip-tags.php

mb_substr() see http://cn2.php.net/manual/en/function.mb-substr.php