code: public function submitButton(SelectorInterface $selector, $additional = false)
      {
          $additional = $additional ? $additional : array();
          foreach ($this->buttons as $button) {
              if ($selector->isMatch($button)) {
                  $encoding = $this->encode();
                  $button->write($encoding);
                  if ($additional) {
                      $encoding->merge($additional);
                  }
  
                  return $encoding;
              }
          }
  
          return false;
      }
docs: Gets the submit values for a selected button.
  
  @param $selector Criteria to apply.
  @param hash $additional Additional data for the form.
  
  @return SimpleEncoding Submitted values or false if there is no such button in the
  form.