Sync docs of selection-coding-system between C and Lisp.

* src/w16select.c (syms_of_win16select) <selection-coding-system>:
* src/w32select.c (syms_of_w32select) <selection-coding-system>:
Sync docs with select.el.
* lisp/select.el (selection-coding-system): Sync doc with C versions.

1 files changed, 29 insertions, 4 deletions

diff --git a/src/w16select.c b/src/w16select.c
index 75d88b558e2..994ad9e543f 100644
--- a/src/w16select.c
+++ b/src/w16select.c
@@ -694,10 +694,35 @@ syms_of_win16select (void)
   defsubr (&Sx_selection_exists_p);
 
   DEFVAR_LISP ("selection-coding-system", &Vselection_coding_system,
-	       doc: /* Coding system for communicating with other X clients.
-When sending or receiving text via cut_buffer, selection, and clipboard,
-the text is encoded or decoded by this coding system.
-The default value is `iso-latin-1-dos'.  */);
+	       doc: /* Coding system for communicating with other programs.
+
+For MS-Windows and MS-DOS:
+When sending or receiving text via selection and clipboard, the text
+is encoded or decoded by this coding system.  The default value is
+the current system default encoding on 9x/Me, `utf-16le-dos'
+\(Unicode) on NT/W2K/XP, and `iso-latin-1-dos' on MS-DOS.
+
+For X Windows:
+When sending text via selection and clipboard, if the target
+data-type matches with the type of this coding system, it is used
+for encoding the text.  Otherwise (including the case that this
+variable is nil), a proper coding system is used as below:
+
+data-type	coding system
+---------	-------------
+UTF8_STRING	utf-8
+COMPOUND_TEXT	compound-text-with-extensions
+STRING		iso-latin-1
+C_STRING	no-conversion
+
+When receiving text, if this coding system is non-nil, it is used
+for decoding regardless of the data-type.  If this is nil, a
+proper coding system is used according to the data-type as above.
+
+See also the documentation of the variable `x-select-request-type' how
+to control which data-type to request for receiving text.
+
+The default value is nil.  */);
   Vselection_coding_system = intern ("iso-latin-1-dos");
 
   DEFVAR_LISP ("next-selection-coding-system", &Vnext_selection_coding_system,