code: public function get($name, $default = null, $first = true)
      {
          $name = strtolower($name);
          if (isset($this->_headers[$name])) {
              return $first ? reset($this->_headers[$name]) : $this->_headers[$name];
          }
  
          return $default;
      }
docs: Returns the named header(s).
  @param string $name the name of the header to return
  @param mixed $default the value to return in case the named header does not exist
  @param bool $first whether to only return the first header of the specified name.
  If false, all headers of the specified name will be returned.
  @return string|array the named header(s). If `$first` is true, a string will be returned;
  If `$first` is false, an array will be returned.