docs: deprecate :ownsyntax

runtime/doc/cmdline.txt

@@ -568,7 +568,6 @@ that see the '"' as part of their argument:
     :menu (and the like)
     :mkspell
     :normal
-    :ownsyntax
     :popup
     :registers
     :return

runtime/doc/deprecated.txt

@@ -26,7 +26,7 @@ DIAGNOSTICS
 
 HIGHLIGHTS
 
-• todo
+• *:ownsyntax* *w:current_syntax*	Use 'winhighlight' instead.
 
 LSP
 

runtime/doc/index.txt

@@ -1473,7 +1473,6 @@ tag		command		action ~
 |:options|	:opt[ions]	open the options-window
 |:ounmap|	:ou[nmap]	like ":unmap" but for Operator-pending mode
 |:ounmenu|	:ounme[nu]	remove menu for Operator-pending mode
-|:ownsyntax|	:ow[nsyntax]	set new local syntax highlight for this window
 |:packadd|	:pa[ckadd]	add a plugin from 'packpath'
 |:packloadall|	:packl[oadall]	load all packages under 'packpath'
 |:pbuffer|	:pb[uffer]	edit buffer in the preview window

runtime/doc/syntax.txt

@@ -5505,38 +5505,7 @@ And put these lines in your vimrc: >
    autocmd BufRead,BufNewFile *.[ch] endif
 
 ==============================================================================
-17. Window-local syntax				*:ownsyntax*
-
-Normally all windows on a buffer share the same syntax settings. It is
-possible, however, to set a particular window on a file to have its own
-private syntax setting. A possible example would be to edit LaTeX source
-with conventional highlighting in one window, while seeing the same source
-highlighted differently (so as to hide control sequences and indicate bold,
-italic etc regions) in another. The 'scrollbind' option is useful here.
-
-To set the current window to have the syntax "foo", separately from all other
-windows on the buffer: >
-   :ownsyntax foo
-<						*w:current_syntax*
-This will set the "w:current_syntax" variable to "foo".  The value of
-"b:current_syntax" does not change.  This is implemented by saving and
-restoring "b:current_syntax", since the syntax files do set
-"b:current_syntax".  The value set by the syntax file is assigned to
-"w:current_syntax".
-Note: This resets the 'spell', 'spellcapcheck', 'spellfile' and 'spelloptions'
-options.
-
-Once a window has its own syntax, syntax commands executed from other windows
-on the same buffer (including :syntax clear) have no effect. Conversely,
-syntax commands executed from that window do not affect other windows on the
-same buffer.
-
-A window with its own syntax reverts to normal behavior when another buffer
-is loaded into that window or the file is reloaded.
-When splitting the window, the new window will use the original syntax.
-
-==============================================================================
-18. Color xterms				*xterm-color* *color-xterm*
+17. Color xterms				*xterm-color* *color-xterm*
 
 							*colortest.vim*
 To test your color setup, a file has been included in the Vim distribution.
@@ -5546,7 +5515,7 @@ To use it, execute this command: >
 Nvim uses 256-color and |true-color| terminal capabilities wherever possible.
 
 ==============================================================================
-19. When syntax is slow						*:syntime*
+18. When syntax is slow						*:syntime*
 
 This is aimed at authors of a syntax file.
 

src/nvim/syntax.c

@@ -5252,6 +5252,7 @@ void ex_syntax(exarg_T *eap)
   }
 }
 
+/// @deprecated
 void ex_ownsyntax(exarg_T *eap)
 {
   if (curwin->w_s == &curwin->w_buffer->b_s) {