Improve documentation of 'invisible-p'

* doc/lispref/display.texi (Invisible Text): Document the return
value of 'invisible-p'.

* src/xdisp.c (Finvisible_p): Rename the argument POS.  Doc fix.
(Bug#29721)

1 files changed, 6 insertions, 1 deletions

diff --git a/doc/lispref/display.texi b/doc/lispref/display.texi
index 7af8d9efb7c..50069e3d1da 100644
--- a/doc/lispref/display.texi
+++ b/doc/lispref/display.texi
@@ -929,13 +929,18 @@ major mode should use the mode's own name as an element of
 
 @defun invisible-p pos-or-prop
 If @var{pos-or-prop} is a marker or number, this function returns a
-non-@code{nil} value if the text at that position is invisible.
+non-@code{nil} value if the text at that position is currently
+invisible.
 
 If @var{pos-or-prop} is any other kind of Lisp object, that is taken
 to mean a possible value of the @code{invisible} text or overlay
 property.  In that case, this function returns a non-@code{nil} value
 if that value would cause text to become invisible, based on the
 current value of @code{buffer-invisibility-spec}.
+
+The return value of this function is @code{t} if the text would be
+completely hidden on display, or a non-@code{nil}, non-@code{t} value
+if the text would be replaced by an ellipsis.
 @end defun
 
 @vindex line-move-ignore-invisible