code: public function getValue(SelectorInterface $selector)
      {
          for ($i = 0, $count = count($this->widgets); $i < $count; $i++) {
              if ($selector->isMatch($this->widgets[$i])) {
                  return $this->widgets[$i]->getValue();
              }
          }
          foreach ($this->buttons as $button) {
              if ($selector->isMatch($button)) {
                  return $button->getValue();
              }
          }
  
          return;
      }
docs: Extracts current value from form.
  
  @param $selector Criteria to apply.
  
  @return string/array Value(s) as string or null if not set.