private function append_str($str)
  { 
    $this->check_closed(); 
    $this->string_buffer .= $str; 
    $len = strlen($str); 
    $this->current_index += $len; 
    return $len; 
  }
private function append_str($str)
  { 
    $this->check_closed(); 
    $this->string_buffer .= $str; 
    $len = strlen($str); 
    $this->current_index += $len; 
    return $len; 
  }
private function append_str ( $ str ) { $ this -> check_closed ( ) ; $ this -> string_buffer .= $ str ; $ len = strlen ( $ str ) ; $ this -> current_index += $ len ; return $ len ; }
Appends bytes to this buffer.
@param string $str
@return integer count of bytes written.
Appends bytes to this buffer .