def register_key_binding(self, keydef, callback_or_cmd, mode='force'):
        """Register a key binding. This takes an mpv keydef and either a string containing a mpv command or a python
        callback function.  See ``MPV.key_binding`` for details.
        """
        if not re.match(r'(Shift+)?(Ctrl+)?(Alt+)?(Meta+)?(.|\w+)', keydef):
            raise ValueError('Invalid keydef. Expected format: [Shift+][Ctrl+][Alt+][Meta+]<key>\n'
                    '<key> is either the literal character the key produces (ASCII or Unicode character), or a '
                    'symbolic name (as printed by --input-keylist')
        binding_name = MPV._binding_name(keydef)
        if callable(callback_or_cmd):
            self._key_binding_handlers[binding_name] = callback_or_cmd
            self.register_message_handler('key-binding', self._handle_key_binding_message)
            self.command('define-section',
                    binding_name, '{} script-binding py_event_handler/{}'.format(keydef, binding_name), mode)
        elif isinstance(callback_or_cmd, str):
            self.command('define-section', binding_name, '{} {}'.format(keydef, callback_or_cmd), mode)
        else:
            raise TypeError('register_key_binding expects either an str with an mpv command or a python callable.')
        self.command('enable-section', binding_name, 'allow-hide-cursor+allow-vo-dragging')
Register a key binding. This takes an mpv keydef and either a string containing a mpv command or a python
        callback function.  See ``MPV.key_binding`` for details.