private static function getRegex()
    {
        if (self::$regex === null) {
            self::$regex = '/('.str_replace('.', '\\.', implode('|', array_keys(self::$suffixes))).')$/';
        }

        return self::$regex;
    }
private static function getRegex()
    {
        if (self::$regex === null) {
            self::$regex = '/('.str_replace('.', '\\.', implode('|', array_keys(self::$suffixes))).')$/';
        }

        return self::$regex;
    }
private static function getRegex ( ) { if ( self :: $ regex === null ) { self :: $ regex = '/(' . str_replace ( '.' , '\\.' , implode ( '|' , array_keys ( self :: $ suffixes ) ) ) . ')$/' ; } return self :: $ regex ; }
Returns the regular expression to detect the file format.

@param string
Returns the regular expression to detect the file format .