1. DomName('Document.execCommand')
  2. DocsEditable()
bool execCommand(String command, bool userInterface, String value)

Source 

@DomName('Document.execCommand')
@DocsEditable()
bool execCommand(String command, bool userInterface, String value) => _blink.BlinkDocument.instance.execCommand_Callback_3_(unwrap_jso(this), command, userInterface, value);