eZ\Publish\Core\FieldType\FieldType::isSingular PHP Method

    public function isSingular()
    {
        return false;
    }

 /**
  * Indicates if the field definition of this type can appear only once in the same ContentType.
  *
  * @return bool
  */
 public function isSingular()
 {
     return $this->internalFieldType->isSingular();
 }