'Help shortcut was pressed. We send a `QWhatsThisClickedEvent` to
the scheme and hope someone responds to it.'

def __on_help_request(self):

    widget = self.sender().parent()
    try:
        node = self.node_for_widget(widget)
    except KeyError:
        pass
    else:
        qualified_name = node.description.qualified_name
        help_url = ('help://search?' + urlencode({'id': qualified_name}))
        event = QWhatsThisClickedEvent(help_url)
        QCoreApplication.sendEvent(self.scheme(), event)
