> I re-re-re-revised mouse-drag-and-drop-region.  I'm sending reply to https://lists.gnu.org/archive/html/emacs-devel/2017-12/msg00258.html, ChangeLog, and patch.
 >
 > * ChangeLog
 >
 > 2017-12-16 Tak Kunihiro <tkk@misasa.okayama-u.ac.jp>
 >
 >          Improve comments and have four new options
 >
 >          * lisp/mouse.el (mouse-drag-and-drop-region): Have option to make dragging cut among buffers. Make usage of tooltip option.
 >          (mouse-drag-and-drop-region-cut-when-buffers-differ): New variable. If non-nil, text is cut instead of copied when dragged among buffers.
 >          (mouse-drag-and-drop-region-show-tooltip): New variable. If non-nil, text is shown by tooltip in a graphic display.
 >          (mouse-drag-and-drop-region-show-cursor): New variable. If non-nil, point is set to where the mouse cursor.
 >          (mouse-drag-and-drop-region-face): New variable for face. The face is used to highlight the original text.

Thanks.  I resend you yet another revised version which mostly fixes the
doc-strings of these options and replaces the option
`mouse-drag-and-drop-region-face' with a face
`mouse-drag-and-drop-region' inheriting from the region face.  Please
have a look.  Unless you or someone else sees problems, I will install
it.

Thanks again for your efforts, martin