master 9cef919692: Improve DND documentation

[Po Lu]

branch: master
commit 9cef919692590e351f52ccee48246bd9d7f4873d
Author: Po Lu <luangruo@yahoo.com>
Commit: Po Lu <luangruo@yahoo.com>

    Improve DND documentation
    
    * doc/lispref/frames.texi (Drag and Drop):
    * src/xfns.c (Fx_begin_drag): Document meaning of
    `XdndActionPrivate'.
---
 doc/lispref/frames.texi | 5 ++++-
 src/xfns.c              | 3 +++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/doc/lispref/frames.texi b/doc/lispref/frames.texi
index 31ebeb51b4..9717fa2978 100644
--- a/doc/lispref/frames.texi
+++ b/doc/lispref/frames.texi
@@ -4070,7 +4070,10 @@ while also being able to drag content to other programs.
 If the drop was rejected or no drop target was found, this function
 returns @code{nil}.  Otherwise, it returns a symbol describing the
 action the target chose to perform, which can differ from @var{action}
-if that isn't supported by the drop target.
+if that isn't supported by the drop target.  @code{XdndActionPrivate}
+is also a valid return value in addition to @code{XdndActionCopy} and
+@code{XdndActionMove}, and means that the drop target chose to perform
+an unspecified action.
 @end defun
 
 @node Color Names
diff --git a/src/xfns.c b/src/xfns.c
index 9d30f2adee..eae409eed2 100644
--- a/src/xfns.c
+++ b/src/xfns.c
@@ -6601,6 +6601,9 @@ can be one of the following:
    `XdndSelection', and to delete whatever was saved into that
    selection afterwards.
 
+`XdndActionPrivate' is also a valid return value, and means that the
+drop target chose to perform an unspecified or unknown action.
+
 There are also some other valid values of ACTION that depend on
 details of both the drop target's implementation details and that of
 Emacs.  For that reason, they are not mentioned here.  Consult