bool required

Source 

@DomName('HTMLSelectElement.required')
@DocsEditable()
bool get required =>
    _blink.BlinkHTMLSelectElement.instance.required_Getter_(this);
void required=(bool value)

Source 

@DomName('HTMLSelectElement.required')
@DocsEditable()
set required(bool value) =>
    _blink.BlinkHTMLSelectElement.instance.required_Setter_(this, value);