Nette\Forms\Rules::setRequired PHP Method

    public function setRequired($value = TRUE)
    {
        if ($value) {
            $this->addRule(Form::REQUIRED, $value === TRUE ? NULL : $value);
        } else {
            $this->required = FALSE;
        }
        return $this;
    }

 /**
  * Makes control mandatory.
  * @param  mixed  state or error message
  * @return self
  */
 public function setRequired($value = TRUE)
 {
     $this->rules->setRequired($value);
     return $this;
 }