Address review comments.

runtime/doc/options.txt

@@ -2356,11 +2356,6 @@ A jump table for the options with a short description can be found at |Q_op|.
 	NOTE: This option is reset when 'compatible' is set.
 	Also see 'preserveindent'.
 
-				*'copytagstack'* *'cptgst'* *'nocopytagstack'* *'nocptgst'*
-'copytagstack' 'cptgst'		boolean	(default: on)
-				global
-	Copy tag stack when splitting window.
-
 						*'cpoptions'* *'cpo'* *cpo*
 'cpoptions' 'cpo'	string	(Vim default: "aABceFsz",
 				 Vi default:  all flags, except "#{|&/\."
@@ -8709,6 +8704,12 @@ A jump table for the options with a short description can be found at |Q_op|.
 	Resetting this option is useful when using a ":tag" command in a
 	mapping which should not change the tagstack.
 
+				*'tagstackcopy'* *'tgstcp'* *'notagstackcopy'* *'notgstcp'*
+'tagstackcopy' 'tgstcp'		boolean	(default: on)
+				global
+	If on, the tagstack is copied from original windows when creating a
+	new one (e.g. via :split). When off, new windows start afresh.
+
 						*'tcldll'*
 'tcldll'		string	(default depends on the build)
 			global

runtime/doc/tags

@@ -765,6 +765,7 @@ $quote	eval.txt	/*$quote*
 'notagbsearch'	options.txt	/*'notagbsearch'*
 'notagrelative'	options.txt	/*'notagrelative'*
 'notagstack'	options.txt	/*'notagstack'*
+'notagstackcopy'	options.txt	/*'notagstackcopy'*
 'notbi'	options.txt	/*'notbi'*
 'notbidi'	options.txt	/*'notbidi'*
 'notbs'	options.txt	/*'notbs'*
@@ -776,6 +777,7 @@ $quote	eval.txt	/*$quote*
 'notf'	options.txt	/*'notf'*
 'notgc'	options.txt	/*'notgc'*
 'notgst'	options.txt	/*'notgst'*
+'notgstcp'	options.txt	/*'notgstcp'*
 'notildeop'	options.txt	/*'notildeop'*
 'notimeout'	options.txt	/*'notimeout'*
 'notitle'	options.txt	/*'notitle'*
@@ -1196,6 +1198,7 @@ $quote	eval.txt	/*$quote*
 'tagrelative'	options.txt	/*'tagrelative'*
 'tags'	options.txt	/*'tags'*
 'tagstack'	options.txt	/*'tagstack'*
+'tagstackcopy'	options.txt	/*'tagstackcopy'*
 'tal'	options.txt	/*'tal'*
 'tb'	options.txt	/*'tb'*
 'tbi'	options.txt	/*'tbi'*
@@ -1222,6 +1225,7 @@ $quote	eval.txt	/*$quote*
 'tfu'	options.txt	/*'tfu'*
 'tgc'	options.txt	/*'tgc'*
 'tgst'	options.txt	/*'tgst'*
+'tgstcp'	options.txt	/*'tgstcp'*
 'thesaurus'	options.txt	/*'thesaurus'*
 'thesaurusfunc'	options.txt	/*'thesaurusfunc'*
 'tildeop'	options.txt	/*'tildeop'*

runtime/doc/tagsrch.txt

@@ -185,6 +185,18 @@ commands explained above the tag stack will look like this:
 The |gettagstack()| function returns the tag stack of a specified window. The
 |settagstack()| function modifies the tag stack of a window.
 
+In Vim, the tag stack is local to each window. When a new tab or window is
+opened (e.g., via |:split| or |:tabnew|), the tag stack is copied from the
+original window.  This allows you to continue tag navigation seamlessly in the
+new window.
+
+If you prefer not to copy the tag stack when splitting windows, set the
+'tagstackcopy' option to off.
+
+Tag navigation commands (such as :tag, :pop, and CTRL-]) affect only the tag
+stack of the current window. Each window maintains its own independent tag
+stack.
+
 							*tagstack-examples*
 Write to the tag stack just like `:tag` but with a user-defined
 jumper#jump_to_tag function: >

src/option.h

@@ -422,7 +422,6 @@ EXTERN char_u	*p_ofu;		// 'omnifunc'
 EXTERN char_u	*p_tsrfu;	// 'thesaurusfunc'
 #endif
 EXTERN int	p_ci;		// 'copyindent'
-EXTERN int	p_cptgst;	// 'copytagstack'
 #if defined(FEAT_GUI) && defined(MACOS_X)
 EXTERN int	*p_antialias;	// 'antialias'
 #endif
@@ -1014,6 +1013,7 @@ EXTERN long	p_tl;		// 'taglength'
 EXTERN int	p_tr;		// 'tagrelative'
 EXTERN char_u	*p_tags;	// 'tags'
 EXTERN int	p_tgst;		// 'tagstack'
+EXTERN int	p_tgstcp;	// 'tagstackcopy'
 #if defined(DYNAMIC_TCL)
 EXTERN char_u	*p_tcldll;	// 'tcldll'
 #endif

src/optiondefs.h

@@ -727,9 +727,6 @@ static struct vimoption options[] =
     {"copyindent",  "ci",   P_BOOL|P_VI_DEF|P_VIM,
 			    (char_u *)&p_ci, PV_CI, NULL, NULL,
 			    {(char_u *)FALSE, (char_u *)0L} SCTX_INIT},
-    {"copytagstack", "cptgst", P_BOOL|P_VIM,
-			    (char_u *)&p_cptgst, PV_NONE, NULL, NULL,
-			    {(char_u *)TRUE, (char_u *)TRUE} SCTX_INIT},
     {"cpoptions",   "cpo",  P_STRING|P_VIM|P_RALL|P_FLAGLIST,
 			    (char_u *)&p_cpo, PV_NONE, did_set_cpoptions, expand_set_cpoptions,
 			    {(char_u *)CPO_VI, (char_u *)CPO_VIM}
@@ -2589,6 +2586,9 @@ static struct vimoption options[] =
     {"tagstack",    "tgst", P_BOOL|P_VI_DEF,
 			    (char_u *)&p_tgst, PV_NONE, NULL, NULL,
 			    {(char_u *)TRUE, (char_u *)0L} SCTX_INIT},
+    {"tagstackcopy", "tgstcp", P_BOOL|P_VIM,
+			    (char_u *)&p_tgstcp, PV_NONE, NULL, NULL,
+			    {(char_u *)TRUE, (char_u *)TRUE} SCTX_INIT},
     {"tcldll",      NULL,   P_STRING|P_EXPAND|P_VI_DEF|P_SECURE,
 #if defined(DYNAMIC_TCL)
 			    (char_u *)&p_tcldll, PV_NONE, NULL, NULL,

src/testdir/Make_all.mak

@@ -114,7 +114,6 @@ NEW_TESTS = \
 	test_compiler \
 	test_conceal \
 	test_const \
-	test_copytagstack \
 	test_cpoptions \
 	test_crash \
 	test_crypt \
@@ -399,7 +398,6 @@ NEW_TESTS_RES = \
 	test_comparators.res \
 	test_conceal.res \
 	test_const.res \
-	test_copytagstack.res \
 	test_cpoptions.res \
 	test_crash.res \
 	test_crypt.res \

src/testdir/test_copytagstack.vim

@@ -1,46 +0,0 @@
-" test 'copytagstack' option
-
-source check.vim
-source view_util.vim
-
-func Test_copytagstack()
-  call writefile(["int Foo;"], 'file.c', 'D')
-  call writefile(["Foo\tfile.c\t1"], 'Xtags', 'D')
-  set tags=Xtags
-
-  tag Foo
-
-  let nr0 = winnr()
-  call assert_equal(1, gettagstack(nr0)['length'])
-
-  split Xtext
-
-  let nr1 = winnr()
-  call assert_equal(1, gettagstack(nr1)['length'])
-
-  set tags&
-  bwipe
-endfunc
-
-func Test_nocopytagstack()
-  call writefile(["int Foo;"], 'file.c', 'D')
-  call writefile(["Foo\tfile.c\t1"], 'Xtags', 'D')
-  set tags=Xtags
-  set nocopytagstack
-
-  tag Foo
-
-  let nr0 = winnr()
-  call assert_equal(1, gettagstack(nr0)['length'])
-
-  split Xtext
-
-  let nr1 = winnr()
-  call assert_equal(0, gettagstack(nr1)['length'])
-
-  set tags&
-  set copytagstack&
-  bwipe
-endfunc
-
-" vim: shiftwidth=2 sts=2 expandtab

src/testdir/test_tagjump.vim

@@ -1671,4 +1671,44 @@ func Test_tag_excmd_with_number_vim9script()
   bwipe!
 endfunc
 
+func Test_tagstackcopy()
+  call writefile(["int Foo;"], 'file.c', 'D')
+  call writefile(["Foo\tfile.c\t1"], 'Xtags', 'D')
+  set tags=Xtags
+
+  tag Foo
+
+  let nr0 = winnr()
+  call assert_equal(1, gettagstack(nr0)['length'])
+
+  split Xtext
+
+  let nr1 = winnr()
+  call assert_equal(1, gettagstack(nr1)['length'])
+
+  set tags&
+  bwipe
+endfunc
+
+func Test_notagstackcopy()
+  call writefile(["int Foo;"], 'file.c', 'D')
+  call writefile(["Foo\tfile.c\t1"], 'Xtags', 'D')
+  set tags=Xtags
+  set notagstackcopy
+
+  tag Foo
+
+  let nr0 = winnr()
+  call assert_equal(1, gettagstack(nr0)['length'])
+
+  split Xtext
+
+  let nr1 = winnr()
+  call assert_equal(0, gettagstack(nr1)['length'])
+
+  set tags&
+  set tagstackcopy&
+  bwipe
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/window.c

@@ -1559,7 +1559,7 @@ win_init(win_T *newp, win_T *oldp, int flags UNUSED)
     }
 
     // copy tagstack and folds
-    if (p_cptgst)
+    if (p_tgstcp)
     {
 	for (i = 0; i < oldp->w_tagstacklen; i++)
 	{