I have re-read the elisp documents and found it is not a problem :-), sorry for disturb...

          A positive integer always relates the left edge of the frame
          to the left edge of its display or parent frame.  A negative
          integer relates the right frame edge to the right edge of the
          display or parent frame.


 






At 2018-02-04 18:02:03, "martin rudalics" <rudalics@gmx.at> wrote:
> > but I think the below result is more useful when I move a child-frame to
> > (0 . -1)
>
>We should not inhibit placement there just as we allow a frame to hide
>the taskbar of the window manager on the desktop.  But we could
>provide a parameter for child frames that would, if set, accomplish
>that.
>
>Could you try coding such a thing?  The value to be added in the
>y-direction should account for the internal border width of the frame,
>the height of the minibuffer, a vertical window divider and the height
>of the mode line if these are set.  In the x-direction we then should
>probably avoid hiding the internal border as well.  And we probably
>should disable the effect of this if it would cause the child frame to
>no more fit into its parent at the top or the right.
>
>martin