1. DomName('HTMLFieldSetElement.setCustomValidity')
  2. DocsEditable()
void setCustomValidity(String error)

Source 

@DomName('HTMLFieldSetElement.setCustomValidity')
@DocsEditable()
void setCustomValidity(String error) => _blink.BlinkHTMLFieldSetElement.instance.setCustomValidity_Callback_1_(this, error);