Subject: [DOC] ‘top-visible’ and‘bottom-visible’ (erroneous indications)

From: Kevin Vigouroux <[email-masked]>
Date: Thu, 16 Dec 2021 06:58:35 +0100

In the Emacs Lisp Reference Manual, section 29.14 Child Frames, a
paragraph contains some errors about ‘top-visible’ and ‘bottom-visible’.

#+begin_quote
The ‘top-visible’ parameter specifies the >>number of pixels at the top
of the frame that always remain visible<< within the parent’s native frame
during dragging and should be set when specifying a non-‘nil’
‘drag-with-header-line’ parameter.  The ‘bottom-visible’ parameter
specifies the >>number of pixels at the bottom of the frame that always
remain visible<< within the parent’s native frame during dragging and
should be preferred when specifying a non-‘nil’ ‘drag-with-mode-line’
parameter.
#+end_quote

The correct description is given in the Emacs Lisp Reference
Manual, section 29.4.3.7 Mouse Dragging Parameters.

#+begin_quote
‘top-visible’
     If this parameter is a number, >>the top edge of the frame never
     appears above the top edge<< of its display or parent frame.
     Moreover, as many pixels of the frame as specified by that number
     will remain visible >>when the frame is moved against any of the
     remaining edges<< of its display or parent frame.  Setting this
     parameter is useful to guard against dragging a child frame with a
     non-‘nil’ ‘drag-with-header-line’ parameter completely out of the
     area of its parent frame.

‘bottom-visible’
     If this parameter is a number, >>the bottom edge of the frame never
     appears below the bottom edge<< of its display or parent frame.
     Moreover, as many pixels of the frame as specified by that number
     will remain visible >>when the frame is moved against any of the
     remaining edges<< of its display or parent frame.  Setting this
     parameter is useful to guard against dragging a child frame with a
     non-‘nil’ ‘drag-with-mode-line’ parameter completely out of the
     area of its parent frame.
#+end_quote

We may move the child frame with the mouse but not above (below) the top
(bottom) edge of the native frame of the parent frame: this is the role
of ‘top-visible’ (‘bottom-visible’) parameter.
-- 
Best regards,
Kevin Vigouroux