src/Form/Container.php
public function isValid()
    {
        $isValid = true;
        foreach ($this->activeForms as $activeFormKey) {
            $activeForm = $this->getForm($activeFormKey);
            $isValid &= $activeForm->isValid();
        }
        return $isValid;
    }
public function isValid()
    {
        $isValid = true;
        foreach ($this->activeForms as $activeFormKey) {
            $activeForm = $this->getForm($activeFormKey);
            $isValid &= $activeForm->isValid();
        }
        return $isValid;
    }
Return isValid

@return bool