def focus_first(self) -> Window | None:
        """Called when the first client in Layout shall be focused.

        This method should:
            - Return the first client in Layout, if any.
            - Not focus the client itself, this is done by caller.
        """
Called when the first client in Layout shall be focused.

        This method should:
            - Return the first client in Layout, if any.
            - Not focus the client itself, this is done by caller.
        
libqtile/layout/base.py