Index: doc/wm.n
==================================================================
--- doc/wm.n
+++ doc/wm.n
@@ -92,11 +92,36 @@
 value accepted by \fBTk_GetColor\fR.  If the empty string is specified
 (default), no transparent color is used.  This is supported on Windows
 2000/XP+.  Where not supported, the \fB\-transparentcolor\fR value remains
 at \fB{}\fR.
 .PP
-On Mac OS X, the following attributes may be set.
+On MacOS, the following attributes may be set.
+.TP
+\fB\-appearance\fR
+.
+Specifies whether the window is rendered in "dark mode".  Allowed
+values are \fBauto\fR, \fBaqua\fR and \fBdarkaqua\fR.  If the setting
+is auto then the appearance of the window is controlled by the
+System Settings.
+.TP
+\fB\-class\fR
+.
+Specifies whether the underlying Aqua window for a toplevel is an
+object of the NSWindow class or the NSPanel class.  The two allowed
+values for this option are \fBnswindow\fR and \fBnspanel\fR.  It is
+not possible to change the class of the underlying Aqua window once
+that window has been instantiated, and attempting to do that is an
+error.  However it is allowed to set this option for a pathname that
+does not correspond to an existing window.  Doing that causes the
+class name to be cached for later use.  When a toplevel with that
+pathname is eventually created, the cached class name will determine which
+class is used for the underlying Aqua window.
+.TP
+\fB\-isdark\fR
+.
+Returns a boolean value which is true if the window is currently in
+dark mode.
 .TP
 \fB\-modified\fR
 .
 Specifies the modification state of the window (determines whether the
 window close widget contains the modification indicator and whether the
@@ -104,14 +129,53 @@
 .TP
 \fB\-notify\fR
 .
 Specifies process notification state (bouncing of the application dock icon).
 .TP
+\fB\-stylemask\fR
+.
+Specifies an integer to be assigned as the styleMask of the underlying
+Aqua window.  (See the Apple documentation for styleMask property of
+the NSWindow class.) The value of this option should be a list of
+bitnames.  Each bit named in the list will be set to 1, and all other
+bits will be set to 0.  The allowed bitnames are: \fBtitled\fR,
+\fBclosable\fR, \fBminiaturizable\fR, \fBresizable\fR,
+\fBfullsizecontentview\fR, \fBdocmodal\fR, \fButility\fR,
+\fBnonactivatingpanel\fR, and \fBHUDwindow\fR.  Note that a side
+effect of setting the fullsizecontentview bit is that the window title
+bar becomes transparent.
+.TP
+\fB\-tabbingid\fR
+.
+Controls how tabbed toplevel windows are grouped together.  Two tabs
+in the same group must correspond to toplevels with the same
+tabbingid, which can be an arbitrary UTF8 string.  In the Tk
+implementation, changing the tabbingid of a toplevel in a tab group
+will cause it to be moved into a different group, in which all tabs
+have the new tabbingid or, if the new tabbingid is unique, to become
+a normal non-tabbed toplevel.   It is allowed to set the tabbingid before the
+toplevel is created.  If the pathname provided in the command does not
+correspond to a toplevel, the value will be cached and used later when
+the toplevel is actually created.
+.TP
+\fB\-tabbingmode\fR
+.
+Controls whether a toplevel can be opened as a tab within a tab group.
+The allowed values are \fBauto\fR, \fBpreferred\fR or
+\fBdisallowed\fR.  A toplevel can be opened as a tab in exactly two
+situations: if its tabbingmode is \fBpreferred\fR; or if its
+tabbingmode is \fBauto\fR and the user has selected "prefer tabs when
+opening documents" in the Desktop and Dock panel of the System
+Settings application.  It is allowed to set the tabbingmode before the
+toplevel is created.  If the pathname provided in the command does not
+correspond to a toplevel, the value will be cached and used later when
+the toplevel is actually created.
+.TP
 \fB\-titlepath\fR
 .
-Specifies the path of the file referenced as the window proxy icon (which
-can be dragged and dropped in lieu of the file's finder icon).
+Specifies the path of the file referenced as the window proxy icon
+(which can be dragged and dropped in lieu of the file's finder icon).
 .TP
 \fB\-transparent\fR
 .
 Makes the window content area transparent and turns off the window shadow. For
 the transparency to be effective, the toplevel background needs to be set to a

Index: generic/tkConfig.c
==================================================================
--- generic/tkConfig.c
+++ generic/tkConfig.c
@@ -2027,22 +2027,24 @@
 	    if (!(optionPtr->specPtr->flags & (TK_OPTION_NULL_OK|TCL_NULL_OK)) || *((int *) internalPtr) != INT_MIN) {
 		objPtr = Tcl_NewWideIntObj(*((int *)internalPtr));
 	    }
 	    break;
 	case TK_OPTION_INDEX:
-	    if (*((int *) internalPtr) == INT_MIN) {
-		objPtr = TkNewIndexObj(TCL_INDEX_NONE);
-	    } else if (*((int *) internalPtr) == INT_MAX) {
-		objPtr = Tcl_NewStringObj("end+1", TCL_INDEX_NONE);
-	    } else if (*((int *) internalPtr) == -1) {
-		objPtr = Tcl_NewStringObj("end", TCL_INDEX_NONE);
-	    } else if (*((int *) internalPtr) < 0) {
-		char buf[32];
-		snprintf(buf, 32, "end%d", 1 + *((int *) internalPtr));
-		objPtr = Tcl_NewStringObj(buf, TCL_INDEX_NONE);
-	    } else {
-		objPtr = Tcl_NewWideIntObj(*((int *) internalPtr));
+	    if (!(optionPtr->specPtr->flags & (TK_OPTION_NULL_OK|TCL_NULL_OK)) || *((int *) internalPtr) != INT_MIN) {
+		if (*((int *) internalPtr) == INT_MIN) {
+		    objPtr = TkNewIndexObj(TCL_INDEX_NONE);
+		} else if (*((int *) internalPtr) == INT_MAX) {
+		    objPtr = Tcl_NewStringObj("end+1", TCL_INDEX_NONE);
+		} else if (*((int *) internalPtr) == -1) {
+		    objPtr = Tcl_NewStringObj("end", TCL_INDEX_NONE);
+		} else if (*((int *) internalPtr) < 0) {
+		    char buf[32];
+		    snprintf(buf, 32, "end%d", 1 + *((int *) internalPtr));
+		    objPtr = Tcl_NewStringObj(buf, TCL_INDEX_NONE);
+		} else {
+		    objPtr = Tcl_NewWideIntObj(*((int *) internalPtr));
+		}
 	    }
 	    break;
 	case TK_OPTION_DOUBLE:
 	    if (!(optionPtr->specPtr->flags & (TK_OPTION_NULL_OK|TCL_NULL_OK)) || !isnan(*((double *) internalPtr))) {
 		objPtr = Tcl_NewDoubleObj(*((double *) internalPtr));

Index: library/demos/mac_styles.tcl
==================================================================
--- library/demos/mac_styles.tcl
+++ library/demos/mac_styles.tcl
@@ -32,12 +32,12 @@
 image create nsimage starry1 -source $starryImg -as file -width 96 -radius 10 -pressed 1
 image create nsimage starry2 -source $starryImg -as file -width 96 -radius 10 -ring 3
 image create nsimage field -source $fieldImg -as file -width 96 -radius 10
 image create nsimage field1 -source $fieldImg -as file -width 96 -radius 10 -pressed 1
 image create nsimage field2 -source $fieldImg -as file -width 96 -radius 10 -ring 3
-image create nsimage add -source NSAddTemplate -width 11 -height 11
-image create nsimage remove -source NSRemoveTemplate -width 11 -height 11
+image create nsimage add -source NSAddTemplate -width 20 -height 20
+image create nsimage remove -source NSRemoveTemplate -width 18 -height 4
 
 # Off state and variables for checkbuttons and radio buttons
 set off {!selected !alternate}
 variable $w.checkVar
 variable $w.radioVar
@@ -128,13 +128,13 @@
  		     -image {bonjour pressed bonjour1}]
 set feather [ttk::button $buttonFrame.feather -style ImageButton -text Tk \
 		      -image {tkfeather pressed tkfeather1}]
 set gradient [ttk::frame $buttonFrame.gradient]
 pack [ttk::button $buttonFrame.gradient.add -style GradientButton \
-		  -image add -padding 7] -side left
+	  -image add -padding {2 0}] -side left
 pack [ttk::button $buttonFrame.gradient.remove -style GradientButton \
-		-image remove -padding 7] -side left
+	  -image remove -padding {2 8}] -side left
 set disclosure [ttk::checkbutton $buttonFrame.disclosure -style DisclosureButton]
 set help [ttk::button $buttonFrame.help -style HelpButton];
 
 $check state $off
 $radio.r1 state $off
@@ -238,24 +238,24 @@
 grid $light -row 1 -column 0 -sticky e
 set dark [ttk::button $appearanceFrame.dark -style ImageButton -text Dark \
 	      -image {starry pressed starry1 selected starry2} \
 	      -command "beDark $appearanceFrame $w"]
 grid $dark -row 1 -column 2 -sticky w
-if { [::tk::unsupported::MacWindowStyle isdark $w] } {
+if { [wm attributes $w -isdark] } {
     $dark state selected
 } else {
     $light state selected
 }
 proc beLight {f w} {
-    ::tk::unsupported::MacWindowStyle appearance $w aqua
+    wm attributes $w -appearance aqua
     $f.dark state !selected
     $f.light state selected
     after 10 $f.light state !hover
 }
 
 proc beDark {f w} {
-    ::tk::unsupported::MacWindowStyle appearance $w darkaqua
+    wm attributes $w -appearance darkaqua
     $f.light state !selected
     $f.dark state selected
     after 10 $f.dark state !hover
 }
 $w.notebook add $appearanceFrame -text "Appearance"

ADDED   library/demos/mac_tabs.tcl
Index: library/demos/mac_tabs.tcl
==================================================================
--- /dev/null
+++ library/demos/mac_tabs.tcl
@@ -0,0 +1,77 @@
+# mac_tabs.tcl --
+#
+# This demonstration script creates three tabbable windows and allows the
+# wm attributes tabbingid and tabbingmode to be manipulated for the third
+# window, to demonstrate the effects of those attributes.
+
+if {![info exists widgetDemo]} {
+    error "This script should be run from the \"widget\" demo."
+}
+
+package require Tk
+catch {font create giant -family {Times New Roman} -size 64}
+set w .mac_tabs
+catch {destroy $w}
+toplevel $w
+package require Tk
+wm title $w "Tabbed Windows in Aqua"
+wm iconname $w "mac_tabs"
+positionWindow $w
+set suffix 0
+set winlist {}
+##
+
+## See Code / Dismiss
+pack [addSeeDismiss $w.buttons $w] -side bottom -fill x
+##
+set info "\
+This demo shows 3 toplevels, A, B, and C.  \
+Each of these has tabbingmode set to preferred. \
+The tabbingid of Window A is groupA, the \
+tabbingid of Window B is groupB and the tabbingid \
+of Window C is groupC.  Use the menubuttons below \
+to see the effect of changing the tabbingid and \
+tabbingmode attributes for Window C. \
+"
+pack [message $w.info -text $info -width 300]
+wm geometry $w +450+350
+
+ttk::frame $w.f
+menu $w.idmenu -tearoff 0
+foreach id {groupA groupB groupC} {
+    $w.idmenu add command -label $id \
+	-command [list wm attributes $w.c -tabbingid $id]
+}
+menu $w.modemenu -tearoff 0
+foreach mode {auto preferred disallowed} {
+    $w.modemenu add command -label $mode \
+	-command [list wm attributes $w.c -tabbingmode $mode]
+}
+ttk::menubutton $w.f.idbutton -menu $w.idmenu -text "tabbingid"\
+    -direction below
+grid $w.f.idbutton -row 0 -column 0
+ttk::menubutton $w.f.modebutton -menu $w.modemenu -text "tabbingmode"\
+    -direction below
+grid $w.f.modebutton -row 1 -column 0
+pack $w.f
+
+wm attributes $w.a -tabbingid groupA
+wm attributes $w.a -tabbingmode preferred
+toplevel $w.a
+wm geometry $w.a +50+100
+wm title $w.a "Window A"
+pack [ttk::label $w.a.l -text A -font giant] -padx 100 -pady 30
+
+wm attributes $w.b -tabbingid groupB
+wm attributes $w.b -tabbingmode preferred
+toplevel $w.b
+wm geometry $w.b +400+100
+wm title $w.b "Window B"
+pack [ttk::label $w.b.l -text B -font giant] -padx 100 -pady 30
+
+wm attributes $w.c -tabbingid groupC
+wm attributes $w.c -tabbingmode preferred
+toplevel $w.c
+wm geometry $w.c +750+100
+wm title $w.c "Window C"
+pack [ttk::label $w.c.l -text C -font giant] -padx 100 -pady 30

ADDED   library/demos/mac_wm.tcl
Index: library/demos/mac_wm.tcl
==================================================================
--- /dev/null
+++ library/demos/mac_wm.tcl
@@ -0,0 +1,228 @@
+# mac_window_styles.tcl --
+#
+# This demonstration script creates a toplevel window containing a notebook
+# whose pages provide examples of the various mac-specific widgets that are
+# provided via special values for the -style option.
+
+if {![info exists widgetDemo]} {
+    error "This script should be run from the \"widget\" demo."
+}
+
+package require Tk
+
+set w .mac_wm
+catch {destroy $w}
+toplevel $w
+package require Tk
+wm title $w "Tk Aqua Window Styles"
+wm iconname $w "mac_wm"
+positionWindow $w
+set suffix 0
+set winlist {}
+##
+
+## See Code / Dismiss
+pack [addSeeDismiss $w.buttons $w] -side bottom -fill x
+
+proc launch {name windowInfo class} {
+    if {[winfo exists $name]} {
+	wm deiconify $name
+	focus -force $name
+	return
+    }
+    wm attributes $name -class $class; toplevel $name
+    wm title $name $class
+    set f $name.f
+    ttk::frame $f
+    set t $f.t
+    text $t -background systemWindowBackgroundColor \
+	-highlightcolor systemWindowBackgroundColor \
+	-font systemDefaultFont\
+	-wrap word -width 50 -height 6
+    $t insert insert $windowInfo
+    $t configure -state disabled
+    grid columnconfigure $f 0 -weight 1
+    grid $t -row 0 -column 0 -columnspan 2 -sticky NSEW
+    ttk::labelframe $f.stylemask -text "styleMask bits"
+    # titled
+    if {$class == "nswindow"} {
+       ttk::checkbutton $f.stylemask.titled -text titled -variable $name.titled \
+          -command [list setbit $name $f.stylemask.titled titled]
+       $f.stylemask.titled state selected
+       grid $f.stylemask.titled -row 0 -column 0 -sticky w
+    }
+    # closable
+    ttk::checkbutton $f.stylemask.closable -text closable -variable $name.closable \
+        -command [list setbit $name $f.stylemask.closable closable]
+    $f.stylemask.closable state selected
+    grid $f.stylemask.closable -row 1 -column 0 -sticky w
+    # miniaturizableable
+    ttk::checkbutton $f.stylemask.miniaturizable -text miniaturizable \
+	-variable $name.miniaturizable \
+        -command [list setbit $name $f.stylemask.miniaturizable miniaturizable]
+    if {$class == "nswindow"} {
+        $f.stylemask.miniaturizable state selected
+    } else {
+        $f.stylemask.miniaturizable state !alternate
+    }
+    grid $f.stylemask.miniaturizable -row 2 -column 0 -sticky w
+    # resizable
+    ttk::checkbutton $f.stylemask.resizable -text resizable -variable $name.resizable \
+	-command [list setbit $name $f.stylemask.resizable resizable]
+    $f.stylemask.resizable state selected
+    grid $f.stylemask.resizable -row 3 -column 0 -sticky w
+    # docmodal
+    ttk::checkbutton $f.stylemask.docmodal -text docmodal -variable $name.docmodal \
+	-command [list setbit $name $f.stylemask.docmodal docmodal]
+    $f.stylemask.docmodal state !alternate
+    grid $f.stylemask.docmodal -row 4 -column 0 -sticky w
+
+    grid $f.stylemask -row 1 -column 0
+    pack $name.f -side bottom -fill both -expand 1 -padx 16 -pady 16
+}
+
+set info "The command wm attributes window -stylemask ?bitnames? can \
+be used to modify bits in the stylemask property of the NSWindow or \
+NSPanel underlying a Tk Window.  Changing these bits causes the \
+style of the window to change.  This demo allows you to see the \
+effects of changing the bits.  (Note that buttons in the title bar \
+can also be enabled or disabled with the ::tk::unsupported::MacWindowStyle \
+command.)"
+
+set panelInfo "A toplevel based on an NSPanel has a narrower title bar\
+than one based on an NSWindow.  In addition the panel remains above all\
+windows on the screen, regardless of which app is active. These are\
+intended to be used as modal windows."
+
+set windowInfo "This is a standard Apple document window, based on an\
+NSWindow.  It has a larger title bar and behaves normally with respect\
+to other windows from the same or another app."
+
+## background frame
+set f $w.f
+ttk::frame $f
+set t $f.t
+text $t -background systemWindowBackgroundColor \
+    -highlightcolor systemWindowBackgroundColor \
+    -font systemDefaultFont\
+    -wrap word -width 50 -height 8
+$t insert insert $info
+$t configure -state disabled
+grid columnconfigure $f 0 -weight 1
+grid $t -row 0 -column 0 -columnspan 2 -sticky NSEW
+ttk::labelframe $f.stylemask -text "styleMask"
+grid $f.stylemask -row 1 -column 0
+grid [ttk::button $f.wbw -text "Open an NSWindow" -width 20 \
+	  -command [list launch .nswindow $windowInfo nswindow]] -row 2 -column 0
+grid [ttk::button $f.wbp -text "Open an NSPanel" -width 20 \
+	  -command [list launch .nspanel $panelInfo nspanel]] -row 3 -column 0
+grid [ttk::button $f.wbm -text "Open a modern window" -width 20 \
+	  -command launchModernWindow] -row 4 -column 0
+pack $w.f -side bottom -fill both -expand 1 -padx 16 -pady 16
+
+proc setbit {win cb bitname} {
+    set state [$cb instate selected]
+    set bits [wm attributes $win -stylemask]
+    set index [lsearch $bits $bitname]
+    if {$index >= 0 && !$state} {
+        set bits [lreplace $bits $index $index]
+    }
+    if {$index < 0 && $state} {
+        lappend bits $bitname
+    }
+    wm attributes $win -stylemask $bits
+}
+
+set aboutText \
+"Most of the apps which ship with a contemporary version of macOS \
+feature a window similar to this one, with a left sidebar that \
+allows selecting the content to be shown on the right hand side of \
+the window.  These windows do not have a (visible) titlebar.\
+\n\nApps that use such windows include the Finder and the App Store as \
+well as Notes, Messages, Books, Maps and many others.\
+\n\nTo create a window like this one in Tk simply set the fullsizecontent bit \
+in the stylemask. For example:\n\n"
+
+set aboutCode \
+"wm attributes .t -stylemask {titled \\\
+\nfullsizecontent closable miniaturizable \\\
+\nresizable}\n\n"
+
+set detailsText \
+"(1) In the Apple API, setting the fullsizecontent bit in the stylemask \
+only allows content to be drawn in the part of the window covered by \
+the titlebar.  In order for that content to be visible the title bar \
+must be transparent.  Since it would be pointless to draw content under \
+an opaque title bar, Tk makes the title bar transparent whenever the \
+fullsizecontent bit is set.\
+
+\n\n\(2) Each radio button in the sidebar is a standard ttk::radiobutton \
+but created with a special value for its -style option.  The value of the \
+-style option used to create these buttons is SidebarButton.\n"
+
+set whichPage 1
+trace add variable whichPage write "flipPage whichPage"
+proc flipPage {varname args} {
+    global whichPage
+    set newpage [set $varname]
+    grid remove [grid content .mod.right -row 0 -column 0]
+    switch $newpage\
+	1 {grid .mod.right.about -padx 30 -pady 30 -row 0 -column 0 -sticky nsew}\
+	2 {grid .mod.right.details -padx 30 -pady 30 -row 0 -column 0 -sticky nsew}
+    update idletasks
+}
+
+proc launchModernWindow {} {
+    global whichPage
+    global aboutText
+    global aboutCode
+    global detailsText
+    if {[winfo exists .mod]} {
+	wm deiconify .mod
+	focus -force .mod
+	return
+    }
+    toplevel .mod
+    wm title .mod {}
+    wm attributes .mod -stylemask {titled fullsizecontent closable \
+				       miniaturizable resizable}
+    .mod configure -background white
+    grid columnconfigure .mod 0 -weight 0
+    grid columnconfigure .mod 1 -weight 1
+    grid rowconfigure .mod 0 -weight 1
+    frame .mod.left -width 220 -height 400 -background systemWindowBackgroundColor
+    catch {
+	font create leftFont -family .AppleSystemUIFont -size 11
+        font create rightFont -family .AppleSystemUIFont -size 16
+        font create codeFont -family Courier -size 16
+    }
+    grid [ttk::label .mod.left.spacer -padding {220 30 0 0}] -row 0 -column 0
+    grid [ttk::radiobutton .mod.left.about -text About -style SidebarButton \
+	      -variable whichPage -value 1] \
+	-row 1 -column 0 -sticky nsew -padx 14
+    grid [ttk::radiobutton .mod.left.details -text Details -style SidebarButton \
+	-variable whichPage -value 2] \
+	-row 2 -column 0 -sticky nsew -padx 14
+    grid .mod.left -row 0 -column 0 -sticky nsew
+    frame .mod.right -width 500 -background systemTextBackgroundColor
+    grid rowconfigure .mod.right 0 -weight 0
+    text .mod.right.about -highlightcolor systemTextBackgroundColor \
+	-background systemTextBackgroundColor -font rightFont \
+	-highlightthickness 0 -wrap word -width 40
+    .mod.right.about tag configure code -font codeFont
+    .mod.right.about insert end $aboutText
+    .mod.right.about insert end $aboutCode code
+    .mod.right.about configure -state disabled
+
+    text .mod.right.details -highlightcolor systemTextBackgroundColor \
+	-background systemTextBackgroundColor -font rightFont\
+	-highlightthickness 0 -wrap word -width 40
+    .mod.right.details insert end $detailsText
+    .mod.right.details configure -state disabled
+
+    grid .mod.right.about -padx 30 -pady 30 -row 0 -column 0 -sticky nsew
+    grid .mod.right -row 0 -column 1 -sticky nsew
+    wm geometry .mod 800x500
+    update idletasks
+}
+

Index: library/demos/widget
==================================================================
--- library/demos/widget
+++ library/demos/widget
@@ -326,16 +326,23 @@
     @@demo image1	Two labels displaying images
     @@demo image2	A simple user interface for viewing images
     @@demo labelframe	Labelled frames
     @@demo ttkbut	The simple Themed Tk widgets
 }
+
 if {[tk windowingsystem] eq "aqua"} {
     addFormattedText {
+	@@subtitle Mac-Specific Widgets and Window Styles
 	@@new
 	@@demo mac_styles	Special widgets for macOS
+	@@new
+	@@demo mac_wm	Window styles for macOS
+	@@new
+	@@demo mac_tabs	Tabbed Windows on macOS
     }
 }
+
 addFormattedText {
     @@subtitle	Listboxes and Trees
     @@demo states	The 50 states
     @@demo colors	Colors: change the color scheme for the application
     @@demo sayings	A collection of famous and infamous sayings

Index: library/ttk/aquaTheme.tcl
==================================================================
--- library/ttk/aquaTheme.tcl
+++ library/ttk/aquaTheme.tcl
@@ -72,10 +72,24 @@
 	    -font {
 		selected RecessedFont
 		active RecessedFont
 		pressed RecessedFont
 	    }
+
+	# Sidebar (radio) button
+	font create SidebarFont -family .AppleSystemUIFont -size 11 -weight normal
+	ttk::style configure SidebarButton \
+	    -foreground systemControlTextColor \
+	    -font SidebarFont
+	ttk::style map SidebarButton \
+	    -foreground {
+		{disabled selected} systemWindowBackgroundColor3
+		{disabled !selected} systemDisabledControlTextColor
+		selected systemTextColor
+		active systemTextColor
+		pressed systemTextColor
+	    }
 
 	# For Entry, Combobox and Spinbox widgets the selected text background
 	# is the "Highlight color" selected in preferences when the widget
 	# has focus.  It is a gray color when the widget does not have focus or
 	# the window does not have focus. (The background state implies !focus

Index: macosx/tkMacOSXMouseEvent.c
==================================================================
--- macosx/tkMacOSXMouseEvent.c
+++ macosx/tkMacOSXMouseEvent.c
@@ -86,11 +86,11 @@
 {
     NSWindow *eventWindow = [theEvent window];
     NSEventType eventType = [theEvent type];
     TKContentView *contentView = [eventWindow contentView];
     NSPoint location = [theEvent locationInWindow];
-    NSPoint viewLocation = [contentView convertPoint:location fromView:nil];
+    //NSPoint viewLocation = [contentView convertPoint:location fromView:nil];
     TkWindow *winPtr = NULL, *grabWinPtr, *scrollTarget = NULL;
     Tk_Window tkwin = NULL, capture, target;
     NSPoint local, global;
     NSInteger button;
     TkWindow *newFocus = NULL;
@@ -115,11 +115,12 @@
      * are recognized by having their timestamp set to 0.  The other is for
      * motion events sent by the local event monitor, which will have their
      * window attribute set to nil.
      */
 
-    if (![eventWindow isMemberOfClass:[TKWindow class]]) {
+    if (![eventWindow isMemberOfClass:[TKWindow class]] &&
+	![eventWindow isMemberOfClass:[TKPanel class]]) {
 	if ([theEvent timestamp] == 0) {
 	    isTestingEvent = YES;
 	    eventWindow = [NSApp keyWindow];
 	}
 	if (eventType == NSLeftMouseDragged ||
@@ -128,11 +129,11 @@
 	    isMotionEvent = YES;
 	}
 	if (!isTestingEvent && !isMotionEvent) {
 	    return theEvent;
 	}
-    } else if (!NSPointInRect(viewLocation, [contentView bounds])) {
+    } else if (!NSPointInRect(location, [contentView bounds])) {
 	isOutside = YES;
     }
     button = [theEvent buttonNumber] + Button1;
     if ((button & -2) == Button2) {
 	button ^= 1; /* Swap buttons 2/3 */
@@ -244,14 +245,14 @@
 	}
 	if (!isTestingEvent) {
 	    NSRect bounds = [contentView bounds];
 	    NSRect grip = NSMakeRect(bounds.size.width - 10, 0, 10, 10);
 	    bounds = NSInsetRect(bounds, 2.0, 2.0);
-	    if (!NSPointInRect(viewLocation, bounds)) {
+	    if (!NSPointInRect(location, bounds)) {
 		return theEvent;
 	    }
-	    if (NSPointInRect(viewLocation, grip)) {
+	    if (NSPointInRect(location, grip)) {
 		return theEvent;
 	    }
 	    if ([NSApp tkLiveResizeEnded]) {
 		[NSApp setTkLiveResizeEnded:NO];
 		return theEvent;

Index: macosx/tkMacOSXPrivate.h
==================================================================
--- macosx/tkMacOSXPrivate.h
+++ macosx/tkMacOSXPrivate.h
@@ -463,10 +463,13 @@
 {
 }
 @property Window tkWindow;
 @end
 
+@interface TKPanel(TKWm)
+- (void)    tkLayoutChanged;
+@end
 #pragma mark NSMenu & NSMenuItem Utilities
 
 @interface NSMenu(TKUtils)
 + (id)menuWithTitle:(NSString *)title;
 + (id)menuWithTitle:(NSString *)title menuItems:(NSArray *)items;

Index: macosx/tkMacOSXSubwindows.c
==================================================================
--- macosx/tkMacOSXSubwindows.c
+++ macosx/tkMacOSXSubwindows.c
@@ -401,11 +401,11 @@
     if (Tk_IsTopLevel(macWin->winPtr) && !Tk_IsEmbedded(macWin->winPtr)) {
 	TKWindow *w = (TKWindow *)macWin->winPtr->wmInfoPtr->window;
 
 	if (w) {
 	    if ([w styleMask] & NSFullScreenWindowMask) {
-		[w tkLayoutChanged];
+		[(TKWindow *)w tkLayoutChanged];
 	    } else {
 		NSRect r = [w contentRectForFrameRect:[w frame]];
 
 		r.origin.y += r.size.height - height;
 		r.size.width = width;

Index: macosx/tkMacOSXWm.c
==================================================================
--- macosx/tkMacOSXWm.c
+++ macosx/tkMacOSXWm.c
@@ -35,11 +35,11 @@
 #define TK_MAC_DEBUG_WINDOWS
 #endif
 */
 
 /*
- * Window attributes and classes
+ * Carbon window attributes and classes.
  */
 
 #define WM_NSMASK_SHIFT 36
 #define tkWindowDoesNotHideAttribute \
 	((UInt64) 1 << kHIWindowBitDoesNotHide)
@@ -109,11 +109,12 @@
 	.styleMask = NSUtilityWindowMask, },
     [kHelpWindowClass] = {
 	.defaultAttrs = kWindowHideOnSuspendAttribute,
 	.forceOnAttrs = kWindowNoTitleBarAttribute |
 		kWindowDoesNotCycleAttribute,
-	.flags = WM_TOPMOST, },
+	.flags = WM_TOPMOST,
+        .styleMask = 0},
     [kSheetWindowClass] = {
 	.validAttrs = kWindowResizableAttribute,
 	.forceOnAttrs = kWindowNoTitleBarAttribute |
 		kWindowDoesNotCycleAttribute,
 	.styleMask = NSDocModalWindowMask, },
@@ -148,23 +149,165 @@
 #define ForceAttributes(attributes, class) \
 	((attributes) & (~macClassAttrs[(class)].forceOffAttrs | \
 	(macClassAttrs[(class)].forceOnAttrs & ~kWindowResizableAttribute)))
 
 /*
- * Data for [wm attributes] command:
+ * Structures and data for the wm attributes command (macOS 10.13 and later):
  */
+
+/* Hash tables for attributes which can be set before a window exists */
+static Tcl_HashTable pathnameToSubclass;
+static Tcl_HashTable pathnameToTabbingId;
+static Tcl_HashTable pathnameToTabbingMode;
+
+enum NSWindowSubclass {
+    subclassNSWindow = 0,
+    subclassNSPanel = 1
+};
+/* This array must be indexed by the enum above.*/
+static const char *subclassNames[] = {"nswindow", "nspanel", NULL};
+
+typedef struct buttonField_t {
+    unsigned zoom: 1;
+    unsigned miniaturize: 1;
+    unsigned close: 1;
+} buttonField;
+
+/* The order of these names must match the order of the bits above! */
+static const char *buttonNames[] = {"zoom", "miniaturize", "close", NULL};
+
+typedef union windowButtonState_t {
+    int intvalue;
+    buttonField bits;
+} windowButtonState;
+
+#if MAC_OS_X_VERSION_MAX_ALLOWED >= 101300
+enum NSWindowClass {
+    NSWindowClass_any = 0,
+    NSWindowClass_window = 1,
+    NSWindowClass_panel = 2
+};
+typedef struct styleMaskBit_t {
+    const char *bitname;
+    unsigned long bitvalue;
+    enum NSWindowClass allowed;
+} styleMaskBit;
+
+static const styleMaskBit styleMaskBits[] = {
+    /* Make the titlebar visible and use round corners. */
+    {"titled", NSWindowStyleMaskTitled, NSWindowClass_window},
+    /* Enable the close button. */
+    {"closable", NSWindowStyleMaskClosable, NSWindowClass_window},
+    /* Enable the miniaturize button. */
+    {"miniaturizable", NSWindowStyleMaskMiniaturizable, NSWindowClass_window},
+    /* Allow the user to resize the window. */
+    {"resizable", NSWindowStyleMaskResizable, NSWindowClass_window},
+    /*
+     * Make the content view extend under the titlebar.  We force
+     * titlebarAppearsTransparent when this bit is set.  Otherwise it is
+     * pretty useless.
+     */
+    {"fullsizecontentview", NSWindowStyleMaskFullSizeContentView, NSWindowClass_window},
+    /* Rounded corners, cannot have a titlebar (overrides titled bit). */
+    {"docmodal", NSWindowStyleMaskDocModalWindow, NSWindowClass_any},
+    /* ============================================
+     * The following bits are only valid for panels.
+     */
+    /* Make the title bar thinner. */
+    {"utility", NSWindowStyleMaskUtilityWindow, NSWindowClass_panel},
+    /* Do not activate the app when the window is activated. */
+    {"nonactivatingpanel", NSWindowStyleMaskNonactivatingPanel, NSWindowClass_panel},
+    /*
+     * Requires utility.  Cannot be resizable.  Close button is an X; no other buttons.
+     * Cannot be a docmodal.
+     */
+    {"HUDwindow", NSWindowStyleMaskHUDWindow, NSWindowClass_panel},
+    {NULL, 0, 0}
+};
+
+typedef struct tabbingMode_t {
+    const char *modeName;
+    long modeValue;
+} tabbingMode;
+
+static const tabbingMode tabbingModes[] = {
+    {"auto",  NSWindowTabbingModeAutomatic},
+    {"disallowed", NSWindowTabbingModeDisallowed},
+    {"preferred", NSWindowTabbingModePreferred},
+    {NULL, -1}
+};
+
+static const char *const appearanceStrings[] = {
+    "aqua", "auto", "darkaqua", NULL
+};
+enum appearances {
+    APPEARANCE_AQUA, APPEARANCE_AUTO, APPEARANCE_DARKAQUA
+};
+
+static Bool wantsToBeTab(NSWindow *macWindow) {
+    Bool result;
+    switch ([macWindow tabbingMode]) {
+    case NSWindowTabbingModeDisallowed:
+	result = False;
+	break;
+    case NSWindowTabbingModePreferred:
+	result = True;
+	break;
+    case NSWindowTabbingModeAutomatic:
+	result = ([NSWindow userTabbingPreference] ==
+		NSWindowUserTabbingPreferenceAlways);
+	break;
+    default:
+	result = False;
+	break;
+    }
+    return result;
+}
+
+/*
+ * Helper for the tkLayoutChanged methods.  Synchronizes Tk's understanding of
+ * the bounds of a contentView with the window's.  It is needed because there
+ * are situations when the window manager can change the layout of an NSWindow
+ * without having been requested to do so by Tk.  Examples are when a window
+ * goes FullScreen or shows a tab bar.  NSWindow methods which involve such
+ * layout changes should be overridden or protected by methods which call this.
+ */
+
+static void syncLayout(NSWindow *macWindow)
+{
+    TkWindow *winPtr = TkMacOSXGetTkWindow(macWindow);
+
+    if (winPtr) {
+	// Using screen coordinates with origin at bottom left.
+	NSRect frameRect = [macWindow frame];
+	// This accounts for the tab bar, if there is one.
+	NSRect contentRect = [macWindow contentRectForFrameRect: frameRect];
+	WmInfo *wmPtr = winPtr->wmInfoPtr;
+
+	// The parent includes the title bar, tab bar and window frame.
+	wmPtr->xInParent = frameRect.origin.x - contentRect.origin.x;
+	wmPtr->yInParent = (frameRect.origin.y + frameRect.size.height -
+	    contentRect.origin.y - contentRect.size.height);
+	wmPtr->parentWidth = winPtr->changes.width + frameRect.size.width -
+	    contentRect.size.width;
+	wmPtr->parentHeight = winPtr->changes.height + frameRect.size.height -
+	    contentRect.size.height;
+    }
+}
+#endif
 
 typedef enum {
-    WMATT_ALPHA, WMATT_FULLSCREEN, WMATT_MODIFIED, WMATT_NOTIFY,
-    WMATT_TITLEPATH, WMATT_TOPMOST, WMATT_TRANSPARENT,
-    WMATT_TYPE, _WMATT_LAST_ATTRIBUTE
+    WMATT_ALPHA, WMATT_APPEARANCE, WMATT_BUTTONS, WMATT_FULLSCREEN,
+    WMATT_ISDARK, WMATT_MODIFIED, WMATT_NOTIFY, WMATT_TITLEPATH, WMATT_TOPMOST,
+    WMATT_TRANSPARENT, WMATT_STYLEMASK, WMATT_CLASS, WMATT_TABBINGID,
+    WMATT_TABBINGMODE, WMATT_TYPE, _WMATT_LAST_ATTRIBUTE
 } WmAttribute;
 
 static const char *const WmAttributeNames[] = {
-    "-alpha", "-fullscreen", "-modified", "-notify",
-    "-titlepath", "-topmost", "-transparent",
-    "-type", NULL
+    "-alpha", "-appearance", "-buttons", "-fullscreen", "-isdark", "-modified",
+    "-notify", "-titlepath", "-topmost", "-transparent", "-stylemask", "-class",
+    "-tabbingid", "-tabbingmode", "-type", NULL
 };
 
 /*
  * The variable below is used to enable or disable tracing in this module. If
  * tracing is enabled, then information is printed on standard output about
@@ -191,11 +334,11 @@
  */
 
 static int tkMacOSXWmAttrNotifyVal = 0;
 
 /*
- * Forward declarations for procedures defined in this file:
+ * Declarations of static functions defined in this file:
  */
 
 static NSRect		InitialWindowBounds(TkWindow *winPtr,
 			    NSWindow *macWindow);
 static int		ParseGeometry(Tcl_Interp *interp, char *string,
@@ -307,12 +450,10 @@
 			    Tcl_Interp *interp, int objc,
 			    Tcl_Obj *const objv[]);
 static void		WmUpdateGeom(WmInfo *wmPtr, TkWindow *winPtr);
 static int		WmWinStyle(Tcl_Interp *interp, TkWindow *winPtr,
 			    int objc, Tcl_Obj *const objv[]);
-static int		WmWinTabbingId(Tcl_Interp *interp, TkWindow *winPtr,
-			    int objc, Tcl_Obj *const objv[]);
 static int		WmWinAppearance(Tcl_Interp *interp, TkWindow *winPtr,
 			    int objc, Tcl_Obj *const objv[]);
 static void		ApplyWindowAttributeFlagChanges(TkWindow *winPtr,
 			    NSWindow *macWindow, UInt64 oldAttributes,
 			    int oldFlags, int create, int initial);
@@ -323,10 +464,94 @@
 static void		GetMaxSize(TkWindow *winPtr, int *maxWidthPtr,
 			    int *maxHeightPtr);
 static void		RemapWindows(TkWindow *winPtr,
 			    MacDrawable *parentWin);
 static void             RemoveTransient(TkWindow *winPtr);
+
+#if MAC_OS_X_VERSION_MAX_ALLOWED > 101300
+
+/*
+ * Add a window as a tab in the group specified by its tabbingid, or
+ * make it a standalone window if it is the only window with that
+ * tabbingid.  Adjust the window size if a tab bar appeared or
+ * disappeared.
+ */
+
+static void placeAsTab(TKWindow *macWindow) {
+    TkWindow *winPtr = NULL, *winPtr2 = NULL;
+    TKWindow *target = NULL, *sibling = NULL;
+    NSString *identifier = [macWindow tabbingIdentifier];
+    if (!wantsToBeTab(macWindow)) {
+	[macWindow moveTabToNewWindow:NSApp];
+	[(TKWindow *)target tkLayoutChanged];
+	return;
+    }
+    for (NSWindow *window in [NSApp windows]) {
+	if (window == macWindow) {
+	    continue;
+	}
+	if ([identifier isEqualTo: [window tabbingIdentifier]] &&
+	    wantsToBeTab(window)) {
+	    target = (TKWindow*) window;
+	    syncLayout(target);
+	    break;
+	}
+    }
+    syncLayout(macWindow);
+    NSArray<NSWindow *> *tabs = [macWindow tabbedWindows];
+    if ([tabs count] == 2) {
+	sibling = tabs[0] == macWindow ? (TKWindow *)tabs[1] : (TKWindow *)tabs[0];
+	syncLayout(sibling);
+	winPtr2 = TkMacOSXGetTkWindow(sibling);
+    }
+    if (target) {
+	CGFloat winHeight = [macWindow contentRectForFrameRect:
+				[macWindow frame]].size.height;
+	CGFloat winDelta = 0, targetHeight, targetDelta = 0;
+	targetHeight =  [target contentRectForFrameRect:
+			    [target frame]].size.height;
+	[target addTabbedWindow:macWindow ordered:NSWindowAbove];
+	targetDelta = targetHeight - [target contentRectForFrameRect:
+					 [target frame]].size.height;
+	winDelta = winHeight - [target contentRectForFrameRect:
+				   [target frame]].size.height;
+	if (winDelta) {
+	    winPtr = TkMacOSXGetTkWindow(macWindow);
+	    XMoveResizeWindow(winPtr->display, winPtr->window,
+			      winPtr->changes.x, winPtr->changes.y,
+			      winPtr->changes.width, winPtr->changes.height + winDelta );
+	    if (sibling) {
+		winPtr = TkMacOSXGetTkWindow(sibling);
+		XMoveResizeWindow(winPtr->display, winPtr->window,
+				  winPtr->changes.x, winPtr->changes.y,
+				  winPtr->changes.width, winPtr->changes.height - winDelta );
+	    }
+	}
+	if (targetDelta) {
+	    winPtr = TkMacOSXGetTkWindow(target);
+	    XMoveResizeWindow(winPtr->display, winPtr->window,
+			      winPtr->changes.x, winPtr->changes.y,
+			      winPtr->changes.width, winPtr->changes.height + targetDelta );
+	}
+    } else {
+	CGFloat height = [macWindow contentRectForFrameRect:
+			     [macWindow frame]].size.height;
+	[macWindow moveTabToNewWindow:NSApp];
+	CGFloat delta = height - [macWindow contentRectForFrameRect:
+			    [macWindow frame]].size.height;
+	winPtr = TkMacOSXGetTkWindow(macWindow);
+	XMoveResizeWindow(winPtr->display, winPtr->window,
+			  winPtr->changes.x, winPtr->changes.y,
+			  winPtr->changes.width, winPtr->changes.height + delta);
+	if (winPtr2) {
+	    XMoveResizeWindow(winPtr2->display, winPtr2->window,
+			      winPtr2->changes.x, winPtr2->changes.y,
+			      winPtr2->changes.width, winPtr2->changes.height + delta );
+	}
+    }
+}
+#endif
 
 #pragma mark NSWindow(TKWm)
 
 @implementation NSWindow(TKWm)
 
@@ -343,23 +568,29 @@
 - (NSPoint) tkConvertPointToScreen: (NSPoint) point
 {
     NSRect pointrect = {point, {0,0}};
     return [self convertRectToScreen:pointrect].origin;
 }
+
 - (NSPoint) tkConvertPointFromScreen: (NSPoint)point
 {
     NSRect pointrect = {point, {0,0}};
     return [self convertRectFromScreen:pointrect].origin;
 }
 #endif
-
 @end
 
 #pragma mark -
 
 @implementation TKPanel: NSPanel
 @synthesize tkWindow = _tkWindow;
+
+- (void) tkLayoutChanged
+{
+    syncLayout(self);
+}
+
 @end
 
 @implementation TKDrawerWindow: NSWindow
 @synthesize tkWindow = _tkWindow;
 @end
@@ -370,48 +601,16 @@
 
 #pragma mark TKWindow(TKWm)
 
 @implementation TKWindow(TKWm)
 
-/*
- * This method synchronizes Tk's understanding of the bounds of a contentView
- * with the window's.  It is needed because there are situations when the
- * window manager can change the layout of an NSWindow without having been
- * requested to do so by Tk.  Examples are when a window goes FullScreen or
- * shows a tab bar.  NSWindow methods which involve such layout changes should
- * be overridden or protected by methods which call this.
- */
-
 - (void) tkLayoutChanged
 {
-    TkWindow *winPtr = TkMacOSXGetTkWindow(self);
-
-    if (winPtr) {
-	NSRect frameRect;
-
-	/*
-	 * This avoids including the title bar for full screen windows
-	 * but does include it for normal windows.
-	 */
-
-	if ([self styleMask] & NSFullScreenWindowMask) {
- 	    frameRect = [NSWindow frameRectForContentRect:NSZeroRect
-		    styleMask:[self styleMask]];
-	} else {
-	    frameRect = [self frameRectForContentRect:NSZeroRect];
-	}
-
-	WmInfo *wmPtr = winPtr->wmInfoPtr;
-
-	wmPtr->xInParent = -frameRect.origin.x;
-	wmPtr->yInParent = frameRect.origin.y + frameRect.size.height;
-	wmPtr->parentWidth = winPtr->changes.width + frameRect.size.width;
-	wmPtr->parentHeight = winPtr->changes.height + frameRect.size.height;
-    }
-}
-
-#if MAC_OS_X_VERSION_MAX_ALLOWED >= 101200
+    syncLayout(self);
+}
+
+#if MAC_OS_X_VERSION_MAX_ALLOWED >= 101300
 - (void)toggleTabBar:(id)sender
 {
     TkWindow *winPtr = TkMacOSXGetTkWindow(self);
     if (!winPtr) {
 	return;
@@ -724,10 +923,12 @@
     wmPtr->attributes = macClassAttrs[kDocumentWindowClass].defaultAttrs;
     wmPtr->scrollWinPtr = NULL;
     wmPtr->menuPtr = NULL;
     wmPtr->window = nil;
     winPtr->wmInfoPtr = wmPtr;
+
+    // initialize wmPtr->NSWindowSubclass here
 
     UpdateVRootGeometry(wmPtr);
 
     /*
      * Tk must monitor structure events for top-level windows, in order to
@@ -1207,20 +1408,43 @@
 
     if (Tcl_GetIndexFromObjStruct(interp, objv[1], optionStrings,
 	    sizeof(char *), "option", 0, &index) != TCL_OK) {
 	return TCL_ERROR;
     }
-
     if (objc < 3) {
 	goto wrongNumArgs;
     }
-
-    if (TkGetWindowFromObj(interp, tkwin, objv[2], (Tk_Window *) &winPtr)
-	!= TCL_OK) {
+    if (index == WMOPT_ATTRIBUTES && objc == 5 &&
+	strcmp(Tcl_GetString(objv[3]), "-class") == 0) {
+	if (TkGetWindowFromObj(NULL, tkwin, objv[2], (Tk_Window *) &winPtr)
+	    == TCL_OK) {
+	    if (winPtr->wmInfoPtr->window != NULL) {
+		Tcl_SetObjResult(interp, Tcl_NewStringObj(
+		    "Cannot change the class after the mac window is created.",-1));
+		Tcl_SetErrorCode(interp, "TK", "CLASS_CHANGE", NULL);
+		return TCL_ERROR;
+	    }
+	} else {
+		winPtr = NULL;
+	}
+    } else if (index == WMOPT_ATTRIBUTES && objc == 5 &&
+	       strcmp(Tcl_GetString(objv[3]), "-tabbingid") == 0) {
+	    if (TkGetWindowFromObj(NULL, tkwin, objv[2], (Tk_Window *) &winPtr)
+		!= TCL_OK) {
+		winPtr = NULL;
+	    }
+    } else if (index == WMOPT_ATTRIBUTES && objc == 5 &&
+	       strcmp(Tcl_GetString(objv[3]), "-tabbingmode") == 0) {
+	    if (TkGetWindowFromObj(NULL, tkwin, objv[2], (Tk_Window *) &winPtr)
+		!= TCL_OK) {
+		winPtr = NULL;
+	    }
+    } else if (TkGetWindowFromObj(interp, tkwin, objv[2], (Tk_Window *) &winPtr)
+	       != TCL_OK) {
 	return TCL_ERROR;
     }
-    if (!Tk_IsTopLevel(winPtr)
+    if (winPtr && !Tk_IsTopLevel(winPtr)
 	    && (index != WMOPT_MANAGE) && (index != WMOPT_FORGET)) {
 	Tcl_SetObjResult(interp, Tcl_ObjPrintf(
 		"window \"%s\" isn't a top-level window", winPtr->pathName));
 	Tcl_SetErrorCode(interp, "TK", "LOOKUP", "TOPLEVEL", winPtr->pathName,
 		NULL);
@@ -1396,10 +1620,11 @@
     WmAttribute attribute,	/* Code of attribute to set */
     Tcl_Obj *value)		/* New value */
 {
     WmInfo *wmPtr = winPtr->wmInfoPtr;
     int boolean;
+    NSString *identifier;
 
     switch (attribute) {
     case WMATT_ALPHA: {
 	double dval;
 
@@ -1416,10 +1641,62 @@
 	} else if (dval > 1.0) {
 	    dval = 1.0;
 	}
 	[macWindow setAlphaValue:dval];
 	break;
+    }
+    case WMATT_APPEARANCE: {
+	int index;
+	if (Tcl_GetIndexFromObjStruct(interp, value, appearanceStrings,
+	    sizeof(char *), "appearancename", 0, &index) != TCL_OK) {
+	    return TCL_ERROR;
+	}
+	switch ((enum appearances) index) {
+	case APPEARANCE_AQUA:
+	    macWindow.appearance = [NSAppearance appearanceNamed:
+		NSAppearanceNameAqua];
+	    break;
+	case APPEARANCE_DARKAQUA:
+#if MAC_OS_X_VERSION_MAX_ALLOWED >= 101400
+	    if (@available(macOS 10.14, *)) {
+		macWindow.appearance = [NSAppearance appearanceNamed:
+		    NSAppearanceNameDarkAqua];
+	    }
+#endif // MAC_OS_X_VERSION_MAX_ALLOWED >= 101400
+	    break;
+	default:
+	    macWindow.appearance = nil;
+	}
+	break;
+    }
+    case WMATT_BUTTONS: {
+	windowButtonState state = {0};
+	Tcl_Obj **elements;
+	Tcl_Size nElements, i;
+	if (Tcl_ListObjGetElements(interp, value, &nElements, &elements) == TCL_OK) {
+	    int index = 0;
+	    for (i = 0; i < nElements; i++) {
+		if (Tcl_GetIndexFromObjStruct(interp, elements[i], buttonNames,
+		       sizeof(char *), "window button name", 0, &index) != TCL_OK) {
+		    return TCL_ERROR;
+		} else {
+		    state.intvalue |= (1 << index);
+		}
+	    }
+	} else if (Tcl_GetIntFromObj(interp, value, &state.intvalue) != TCL_OK) {
+	    return TCL_ERROR;
+	}
+	NSButton *closer = [macWindow standardWindowButton:
+			       NSWindowCloseButton];
+	NSButton *miniaturizer = [macWindow standardWindowButton:
+				     NSWindowMiniaturizeButton];
+	NSButton *zoomer = [macWindow standardWindowButton:
+			      NSWindowZoomButton];
+	closer.enabled = (state.bits.close != 0);
+	miniaturizer.enabled = (state.bits.miniaturize != 0);
+	zoomer.enabled = (state.bits.zoom != 0);
+	break;
     }
     case WMATT_FULLSCREEN:
 	if (Tcl_GetBooleanFromObj(interp, value, &boolean) != TCL_OK) {
 	    return TCL_ERROR;
 	}
@@ -1454,10 +1731,125 @@
 		request = [NSApp requestUserAttention:NSCriticalRequest];
 	    }
 	    tkMacOSXWmAttrNotifyVal = boolean;
 	}
 	break;
+    case WMATT_STYLEMASK: {
+	unsigned long styleMaskValue = 0;
+	Tcl_Obj **elements;
+	Tcl_Size nElements, i;
+	if (Tcl_ListObjGetElements(interp, value, &nElements, &elements) == TCL_OK) {
+	    int index;
+	    for (i = 0; i < nElements; i++) {
+		if (Tcl_GetIndexFromObjStruct(interp, elements[i], styleMaskBits,
+		       sizeof(styleMaskBit), "styleMask bit", 0, &index) != TCL_OK) {
+		    return TCL_ERROR;
+		} else if (![macWindow isKindOfClass: [NSPanel class]] &&
+			   styleMaskBits[index].allowed == NSWindowClass_panel) {
+		    Tcl_SetObjResult(interp, Tcl_ObjPrintf(
+		        "styleMask bit \"%s\" can only be used with an NSPanel",
+			styleMaskBits[index].bitname));
+		    Tcl_SetErrorCode(interp, "TK", "INVALID_STYLEMASK_BIT", NULL);
+		    return TCL_ERROR;
+		} else {
+		    styleMaskValue |= styleMaskBits[index].bitvalue;
+		}
+		/*
+		 * Be sure not to change the fullscreen bit.
+		 */
+		styleMaskValue |= (NSWindowStyleMaskFullScreen & macWindow.styleMask);
+	    }
+	    /*
+	     * A resizable docmodal NSWindow or NSPanel does not work
+	     * correctly.  It cannot be resized from the top edge.  Other bits,
+	     * such as titled are ignored for docmodals.  To be safe, we clear
+	     * all other bits when the docmodal bit is set.
+	     */
+	    if (styleMaskValue & NSDocModalWindowMask) {
+		styleMaskValue &= ~NSWindowStyleMaskResizable;
+	    }
+	    if ([macWindow isKindOfClass: [NSPanel class]]) {
+		/*
+		 * We always make NSPanels titled, nonactivating utility windows,
+		 * even if these bits are not requested in the command.
+		 */
+		if (!(styleMaskValue & NSWindowStyleMaskTitled) ) {
+		    styleMaskValue |= NSWindowStyleMaskTitled;
+		    styleMaskValue |= NSWindowStyleMaskUtilityWindow;
+		    styleMaskValue |= NSWindowStyleMaskNonactivatingPanel;
+		}
+	    }
+	    if (styleMaskValue & NSWindowStyleMaskFullSizeContentView) {
+		macWindow.titlebarAppearsTransparent = YES;
+	    } else {
+		macWindow.titlebarAppearsTransparent = NO;
+	    }
+	} else {
+	    return TCL_ERROR;
+	}
+	NSRect oldFrame = [macWindow frame];
+#ifdef DEBUG
+	fprintf(stderr, "Current styleMask: %lx\n", [macWindow styleMask]);
+	fprintf(stderr, "Setting styleMask to %lx\n", styleMaskValue);
+#endif
+        macWindow.styleMask = (unsigned long) styleMaskValue;
+	NSRect newFrame = [macWindow frame];
+	int heightDiff = newFrame.size.height - oldFrame.size.height;
+	int newHeight = heightDiff < 0 ? newFrame.size.height :
+	    newFrame.size.height - heightDiff;
+	[(TKWindow *)macWindow tkLayoutChanged];
+	if (heightDiff) {
+	    //Calling XMoveResizeWindow twice is a hack to force a relayout
+	    //of the window.
+	    XMoveResizeWindow(winPtr->display, winPtr->window,
+	 		  winPtr->changes.x, winPtr->changes.y,
+			  newFrame.size.width, newHeight - 1);
+	    XMoveResizeWindow(winPtr->display, winPtr->window,
+	 		  winPtr->changes.x, winPtr->changes.y,
+			  newFrame.size.width, newHeight);
+	}
+	break;
+    }
+    case WMATT_TABBINGID: {
+	NSString *oldId = [macWindow tabbingIdentifier];
+	char *valueString;
+	int length;
+	if ([NSApp macOSVersion] < 101300) {
+	    Tcl_SetObjResult(interp, Tcl_NewStringObj(
+		  "Tabbing identifiers require macOS 10.13", TCL_INDEX_NONE));
+	    Tcl_SetErrorCode(interp, "TK", "WM", "TABBINGID", NULL);
+	    return TCL_ERROR;
+	}
+	valueString = Tcl_GetStringFromObj(value, &length);
+	identifier = [NSString stringWithUTF8String:valueString];
+	[macWindow setTabbingIdentifier: identifier];
+
+	/*
+	 * If the tabbingIdentifier of a tab is changed we move it into
+	 * the tab group with that identifier.
+	 */
+
+	if ([oldId compare:identifier] != NSOrderedSame) {
+	    placeAsTab((TKWindow *)macWindow);
+	}
+	break;
+    }
+    case WMATT_TABBINGMODE: {
+	int index;
+	tabbingMode mode;
+	if (Tcl_GetIndexFromObjStruct(interp, value, tabbingModes,
+	   sizeof(tabbingMode), "NSWindow Tabbing Mode", 0, &index) != TCL_OK) {
+		return TCL_ERROR;
+	    }
+	mode = tabbingModes[index];
+	[macWindow setTabbingMode: mode.modeValue];
+	placeAsTab((TKWindow *)macWindow);
+	break;
+    }
+    case WMATT_ISDARK: {
+	break;
+    }
     case WMATT_TITLEPATH: {
 	const char *path = (const char *)Tcl_FSGetNativePath(value);
 	NSString *filename = @"";
 
 	if (path && *path) {
@@ -1503,10 +1895,12 @@
 	    [macWindow setOpaque:!boolean];
 	    TkMacOSXInvalidateWindow((MacDrawable *)winPtr->window,
 		    TK_PARENT_WINDOW);
 	    }
 	break;
+    case WMATT_CLASS:
+	break;
     case WMATT_TYPE:
 	TKLog(@"The type attribute is ignored on macOS.");
 	break;
     case _WMATT_LAST_ATTRIBUTE:
     default:
@@ -1536,20 +1930,93 @@
     WmInfo *wmPtr = winPtr->wmInfoPtr;
 
     switch (attribute) {
     case WMATT_ALPHA:
 	result = Tcl_NewDoubleObj([macWindow alphaValue]);
+	break;
+    case WMATT_APPEARANCE: {
+#if MAC_OS_X_VERSION_MAX_ALLOWED >= 101300
+	NSAppearanceName appearance;
+#else
+	NSString *appearance;
+#endif // MAC_OS_X_VERSION_MAX_ALLOWED >= 101300
+	const char *resultString = "unrecognized";
+	appearance = macWindow.appearance.name;
+	if (appearance == nil) {
+	    resultString = appearanceStrings[APPEARANCE_AUTO];
+	} else if (appearance == NSAppearanceNameAqua) {
+	    resultString = appearanceStrings[APPEARANCE_AQUA];
+#if MAC_OS_X_VERSION_MAX_ALLOWED >= 101400
+	} else if (@available(macOS 10.14, *)) {
+	    if (appearance == NSAppearanceNameDarkAqua) {
+		resultString = appearanceStrings[APPEARANCE_DARKAQUA];
+	    }
+#endif // MAC_OS_X_VERSION_MAX_ALLOWED >= 101400
+	}
+	result = Tcl_NewStringObj(resultString, TCL_INDEX_NONE);
+	break;
+    }
+    case WMATT_BUTTONS: {
+	result = Tcl_NewListObj(3, NULL);
+	if ([macWindow standardWindowButton:NSWindowCloseButton].enabled) {
+	    Tcl_ListObjAppendElement(NULL, result, Tcl_NewStringObj("close", TCL_INDEX_NONE));
+	}
+	if ([macWindow standardWindowButton:NSWindowMiniaturizeButton].enabled) {
+	    Tcl_ListObjAppendElement(NULL, result, Tcl_NewStringObj("miniaturize", TCL_INDEX_NONE));
+	}
+	if ([macWindow standardWindowButton:NSWindowZoomButton].enabled) {
+	    Tcl_ListObjAppendElement(NULL, result, Tcl_NewStringObj("zoom", TCL_INDEX_NONE));
+	}
+	break;
+    }
+    case WMATT_CLASS:
+	if ([macWindow isKindOfClass:[NSPanel class]]) {
+	    result = Tcl_NewStringObj(subclassNames[subclassNSPanel], TCL_INDEX_NONE);
+	} else {
+	    result = Tcl_NewStringObj(subclassNames[subclassNSWindow], TCL_INDEX_NONE);
+	}
 	break;
     case WMATT_FULLSCREEN:
 	result = Tcl_NewBooleanObj([macWindow styleMask] & NSFullScreenWindowMask);
 	break;
+    case WMATT_ISDARK:
+	result = Tcl_NewBooleanObj(TkMacOSXInDarkMode((Tk_Window)winPtr));
+	break;
     case WMATT_MODIFIED:
 	result = Tcl_NewBooleanObj([macWindow isDocumentEdited]);
 	break;
     case WMATT_NOTIFY:
 	result = Tcl_NewBooleanObj(tkMacOSXWmAttrNotifyVal);
 	break;
+    case WMATT_STYLEMASK: {
+	unsigned long styleMaskValue = [macWindow styleMask];
+	const styleMaskBit *bit;
+	result = Tcl_NewListObj(9, NULL);
+	for (bit = styleMaskBits; bit->bitname != NULL; bit++) {
+	    if (styleMaskValue & bit->bitvalue) {
+		Tcl_ListObjAppendElement(NULL, result,
+		    Tcl_NewStringObj(bit->bitname, TCL_INDEX_NONE));
+	    }
+	}
+	break;
+    }
+    case WMATT_TABBINGID:
+	result = Tcl_NewStringObj([[macWindow tabbingIdentifier] UTF8String],
+		-1);
+	break;
+    case WMATT_TABBINGMODE: {
+	long mode = [macWindow tabbingMode];
+	const char *name = "unrecognized";
+	for (const tabbingMode *m = tabbingModes; m->modeName != NULL; m++) {
+	    if (m->modeValue == mode) {
+		name = m->modeName;
+		break;
+	    }
+	}
+	result = Tcl_NewStringObj(name, TCL_INDEX_NONE);
+	break;
+    }
     case WMATT_TITLEPATH:
 	result = Tcl_NewStringObj([[macWindow representedFilename] UTF8String],
 		TCL_INDEX_NONE);
 	break;
     case WMATT_TOPMOST:
@@ -1585,20 +2052,70 @@
  *----------------------------------------------------------------------
  */
 
 static int
 WmAttributesCmd(
-    TCL_UNUSED(Tk_Window),		/* Main window of the application. */
+    TCL_UNUSED(Tk_Window),	/* Main window of the application. */
     TkWindow *winPtr,		/* Toplevel to work with */
     Tcl_Interp *interp,		/* Current interpreter. */
     int objc,			/* Number of arguments. */
     Tcl_Obj *const objv[])	/* Argument objects. */
 {
     int attribute = 0;
     NSWindow *macWindow;
+    if (winPtr == NULL && objc == 5) {
+	int index, isNew = 0, length;
 
-    if (winPtr->window == None) {
+	/*
+	 * If we are setting an atttribute of a future window, save the value
+	 * in a hash table so we can look it up when the window is actually
+	 * created.
+	 */
+
+	if (strcmp(Tcl_GetString(objv[3]), "-class") == 0) {
+	    if (Tcl_GetIndexFromObjStruct(interp, objv[4], subclassNames,
+		    sizeof(char *), "NSWindow subclass", 0, &index) != TCL_OK) {
+		return TCL_ERROR;
+	    }
+	    Tcl_HashEntry *hPtr = Tcl_CreateHashEntry(&pathnameToSubclass,
+		Tcl_GetString(objv[2]), &isNew);
+	    if (hPtr) {
+		Tcl_SetHashValue(hPtr, INT2PTR(index));
+		return TCL_OK;
+	    }
+	} else if (strcmp(Tcl_GetString(objv[3]), "-tabbingid") == 0) {
+	    char *identifier = Tcl_GetStringFromObj(objv[4], &length);
+	    char *value = ckalloc(length + 1);
+	    strncpy(value, identifier, length + 1);
+	    Tcl_HashEntry *hPtr = Tcl_CreateHashEntry(&pathnameToTabbingId,
+				      Tcl_GetString(objv[2]), &isNew);
+	    if (hPtr) {
+		Tcl_SetHashValue(hPtr, value);
+		return TCL_OK;
+	    }
+	} else if (strcmp(Tcl_GetString(objv[3]), "-tabbingmode") == 0) {
+	    long value = NSWindowTabbingModeAutomatic;
+	    int modeIndex;
+	    if (Tcl_GetIndexFromObjStruct(interp, objv[4], tabbingModes,
+	       sizeof(tabbingMode), "NSWindow Tabbing Mode", 0, &modeIndex) == TCL_OK) {
+		value = tabbingModes[modeIndex].modeValue;
+	    }
+	    Tcl_HashEntry *hPtr = Tcl_CreateHashEntry(&pathnameToTabbingMode,
+		Tcl_GetString(objv[2]), &isNew);
+	    if (hPtr) {
+		Tcl_SetHashValue(hPtr, value);
+		return TCL_OK;
+	    }
+	}
+    }
+    if (!winPtr) {
+	Tcl_SetObjResult(interp, Tcl_ObjPrintf(
+	   "Only -class, -tabbingid, or -tabbingmode can be set before the window exists."));
+	Tcl_SetErrorCode(interp, "TK", "NO_WINDOW", NULL);
+	return TCL_ERROR;
+    }
+    if (winPtr && winPtr->window == None) {
 	Tk_MakeWindowExist((Tk_Window)winPtr);
     }
     if (!TkMacOSXHostToplevelExists(winPtr)) {
 	TkMacOSXMakeRealWindowExist(winPtr);
     }
@@ -3095,11 +3612,11 @@
  *----------------------------------------------------------------------
  */
 
 static int
 WmOverrideredirectCmd(
-    TCL_UNUSED(Tk_Window),		/* Main window of the application. */
+    TCL_UNUSED(Tk_Window),	/* Main window of the application. */
     TkWindow *winPtr,		/* Toplevel to work with */
     Tcl_Interp *interp,		/* Current interpreter. */
     int objc,			/* Number of arguments. */
     Tcl_Obj *const objv[])	/* Argument objects. */
 {
@@ -3121,11 +3638,19 @@
     if (Tcl_GetBooleanFromObj(interp, objv[3], &flag) != TCL_OK) {
 	return TCL_ERROR;
     }
     atts.override_redirect = flag ? True : False;
     Tk_ChangeWindowAttributes((Tk_Window)winPtr, CWOverrideRedirect, &atts);
-    ApplyContainerOverrideChanges(winPtr, win);
+    if ([NSApp macOSVersion] >= 101300) {
+	if (flag) {
+	    win.styleMask |= NSWindowStyleMaskDocModalWindow;
+	} else {
+	    win.styleMask &= ~NSWindowStyleMaskDocModalWindow;
+	}
+    } else {
+	ApplyContainerOverrideChanges(winPtr, win);
+    }
     return TCL_OK;
 }
 
 /*
  *----------------------------------------------------------------------
@@ -5670,14 +6195,14 @@
     Tcl_Interp *interp,		/* Current interpreter. */
     int objc,			/* Number of arguments. */
     Tcl_Obj *const objv[])	/* Argument objects. */
 {
     static const char *const subcmds[] = {
-	"appearance", "isdark", "style", "tabbingid", NULL
+	"appearance", "isdark", "style", NULL
     };
     enum SubCmds {
-	TKMWS_APPEARANCE, TKMWS_ISDARK, TKMWS_STYLE, TKMWS_TABID
+	TKMWS_APPEARANCE, TKMWS_ISDARK, TKMWS_STYLE
     };
     Tk_Window tkwin = (Tk_Window)clientData;
     TkWindow *winPtr;
     int index;
 
@@ -5707,22 +6232,10 @@
 	if ((objc < 3) || (objc > 5)) {
 	    Tcl_WrongNumArgs(interp, 2, objv, "window ?class attributes?");
 	    return TCL_ERROR;
 	}
 	return WmWinStyle(interp, winPtr, objc, objv);
-    case TKMWS_TABID:
-	if ([NSApp macOSVersion] < 101200) {
-	    Tcl_SetObjResult(interp, Tcl_NewStringObj(
-                "Tabbing identifiers did not exist until OSX 10.12.", TCL_INDEX_NONE));
-	    Tcl_SetErrorCode(interp, "TK", "WINDOWSTYLE", "TABBINGID", NULL);
-	    return TCL_ERROR;
-	}
-	if ((objc < 3) || (objc > 4)) {
-	    Tcl_WrongNumArgs(interp, 2, objv, "window ?newid?");
-	    return TCL_ERROR;
-	}
-	return WmWinTabbingId(interp, winPtr, objc, objv);
     case TKMWS_APPEARANCE:
 	if ([NSApp macOSVersion] < 100900) {
 	    Tcl_SetObjResult(interp, Tcl_NewStringObj(
                 "Window appearances did not exist until OSX 10.9.", TCL_INDEX_NONE));
 	    Tcl_SetErrorCode(interp, "TK", "WINDOWSTYLE", "APPEARANCE", NULL);
@@ -5938,91 +6451,10 @@
 }
 
 /*
  *----------------------------------------------------------------------
  *
- * WmWinTabbingId --
- *
- *	This procedure is invoked to process the
- *	"::tk::unsupported::MacWindowStyle tabbingid" subcommand. The command
- *	allows you to get or set the tabbingIdentifier for the NSWindow
- *	associated with a Tk Window.  The syntax is:
- *
- *	    tk::unsupported::MacWindowStyle tabbingid window ?newId?
- *
- * Results:
- *	Returns the tabbingIdentifier of the window prior to calling this
- *      function.  If the optional newId argument is omitted, the window's
- *      tabbingIdentifier is not changed.
- *
- * Side effects:
- *	Windows may only be grouped together as tabs if they all have the same
- *      tabbingIdentifier.  In particular, by giving a window a unique
- *      tabbingIdentifier one can prevent it from becoming a tab in any other
- *      window.  Changing the tabbingIdentifier of a window which is already
- *      a tab causes it to become a separate window.
- *
- *----------------------------------------------------------------------
- */
-
-static int
-WmWinTabbingId(
-    Tcl_Interp *interp,		/* Current interpreter. */
-    TkWindow *winPtr,		/* Window to be manipulated. */
-    int objc,			/* Number of arguments. */
-    Tcl_Obj * const objv[])	/* Argument objects. */
-{
-#if MAC_OS_X_VERSION_MAX_ALLOWED < 101200
-    (void) interp;
-    (void) winPtr;
-    (void) objc;
-    (void) objv;
-    return TCL_OK;
-#else
-    Tcl_Obj *result = NULL;
-    NSString *idString;
-    NSWindow *win = TkMacOSXGetNSWindowForDrawable(winPtr->window);
-    if (win) {
-	idString = win.tabbingIdentifier;
-	result = Tcl_NewStringObj(idString.UTF8String, [idString length]);
-    }
-    if (result == NULL) {
-	NSLog(@"Failed to read tabbing identifier; try calling update idletasks"
-	      " before getting/setting the tabbing identifier of the window.");
-	return TCL_OK;
-    }
-    Tcl_SetObjResult(interp, result);
-    if (objc == 3) {
-	return TCL_OK;
-    } else if (objc == 4) {
-	int len;
-	char *newId = Tcl_GetStringFromObj(objv[3], &len);
-	NSString *newIdString = [NSString stringWithUTF8String:newId];
-	[win setTabbingIdentifier: newIdString];
-
-	/*
-	 * If the tabbingIdentifier of a tab is changed we also turn it into a
-	 * separate window so we don't violate the rule that all tabs in the
-	 * same frame must have the same tabbingIdentifier.
-	 */
-
-	if ([idString compare:newIdString] != NSOrderedSame
-#if MAC_OS_X_VERSION_MIN_REQUIRED > 101200
-		&& [win tab]
-#endif
-		) {
-	    [win moveTabToNewWindow:nil];
-	}
-	return TCL_OK;
-    }
-    return TCL_ERROR;
-#endif
-}
-
-/*
- *----------------------------------------------------------------------
- *
  * WmWinAppearance --
  *
  *	This procedure is invoked to process the
  *	"::tk::unsupported::MacWindowStyle appearance" subcommand. The command
  *	allows you to get or set the appearance for the NSWindow associated
@@ -6061,16 +6493,10 @@
     (void) winPtr;
     (void) objc;
     (void) objv;
     return TCL_OK;
 #else
-    static const char *const appearanceStrings[] = {
-	"aqua", "auto", "darkaqua", NULL
-    };
-    enum appearances {
-	APPEARANCE_AQUA, APPEARANCE_AUTO, APPEARANCE_DARKAQUA
-    };
     Tcl_Obj *result = NULL;
 #if MAC_OS_X_VERSION_MAX_ALLOWED >= 101300
     NSAppearanceName appearance;
 #else
     NSString *appearance;
@@ -6185,11 +6611,18 @@
     TkWindow *winPtr)		/* Tk window. */
 {
     WmInfo *wmPtr = winPtr->wmInfoPtr;
     MacDrawable *macWin;
     WindowClass macClass;
+    Class winClass = nil;
     Bool overrideRedirect = Tk_Attributes((Tk_Window)winPtr)->override_redirect;
+    Tcl_HashEntry *hPtr = NULL;
+    NSUInteger styleMask;
+    NSString *identifier;
+    char *tabbingId = NULL;
+    long tabbingMode = NSWindowTabbingModeAutomatic;
+    static int initialized = 0;
 
     if (TkMacOSXHostToplevelExists(winPtr)) {
 	return;
     }
 
@@ -6216,55 +6649,121 @@
 	/*
 	 * TODO: Here we should handle out of process embedding.
 	 */
     }
 
-    /*
-     * If this is an override-redirect window, the NSWindow is created first as
-     * a document window then converted to a simple window.
-     */
-
-    if (overrideRedirect) {
-	wmPtr->macClass = kDocumentWindowClass;
-    }
-    macClass = wmPtr->macClass;
-    wmPtr->attributes &= (tkAlwaysValidAttributes |
-	    macClassAttrs[macClass].validAttrs);
-    wmPtr->flags |= macClassAttrs[macClass].flags |
+    if ([NSApp macOSVersion] >= 101300) {
+	/*
+	 * Prior to macOS 10.12 the styleMask was readonly.  From macOS 10.12
+	 * onward, the styleMask can replace the Carbon window classes and
+	 * attributes.
+	 */
+	int index;
+	if (!initialized) {
+	    Tcl_InitHashTable(&pathnameToSubclass, TCL_STRING_KEYS);
+	    Tcl_InitHashTable(&pathnameToTabbingId, TCL_STRING_KEYS);
+	    Tcl_InitHashTable(&pathnameToTabbingMode, TCL_STRING_KEYS);
+	    initialized = 1;
+	}
+	hPtr = Tcl_FindHashEntry(&pathnameToSubclass, Tk_PathName(winPtr));
+	index = hPtr ? PTR2INT(Tcl_GetHashValue(hPtr)) : subclassNSWindow;
+	switch(index) {
+	case subclassNSPanel:
+	    winClass = [TKPanel class];
+	    styleMask =  (NSWindowStyleMaskTitled        |
+			  NSWindowStyleMaskClosable      |
+			  NSWindowStyleMaskResizable     |
+			  NSWindowStyleMaskUtilityWindow |
+			  NSWindowStyleMaskNonactivatingPanel );
+		break;
+	default:
+	    winClass = [TKWindow class];
+	    styleMask =  (NSWindowStyleMaskTitled         |
+			  NSWindowStyleMaskClosable       |
+			  NSWindowStyleMaskMiniaturizable |
+			  NSWindowStyleMaskResizable );
+		break;
+	}
+	if (overrideRedirect) {
+	    styleMask |= NSWindowStyleMaskDocModalWindow;
+	}
+	/* Help windows (used for tooltips) should have stylemask 0. */
+	if (wmPtr->macClass == kHelpWindowClass) {
+	    styleMask = 0;
+	}
+	if (hPtr) {
+	    Tcl_DeleteHashEntry(hPtr);
+	}
+	hPtr = Tcl_FindHashEntry(&pathnameToTabbingId, Tk_PathName(winPtr));
+	if (hPtr) {
+	    tabbingId = Tcl_GetHashValue(hPtr);
+	    Tcl_DeleteHashEntry(hPtr);
+	    ckfree(tabbingId);
+	}
+	hPtr = Tcl_FindHashEntry(&pathnameToTabbingMode, Tk_PathName(winPtr));
+	if (hPtr) {
+	    tabbingMode = PTR2INT(Tcl_GetHashValue(hPtr));
+	    Tcl_DeleteHashEntry(hPtr);
+	}
+    } else {
+
+	/*
+	 * If this is an override-redirect window, the NSWindow is created first as
+	 * a document window then converted to a simple window.
+	 */
+
+	if (overrideRedirect) {
+	    wmPtr->macClass = kDocumentWindowClass;
+	}
+	macClass = wmPtr->macClass;
+	wmPtr->attributes &= (tkAlwaysValidAttributes |
+			      macClassAttrs[macClass].validAttrs);
+	wmPtr->flags |= macClassAttrs[macClass].flags |
 	    ((wmPtr->attributes & kWindowResizableAttribute) ? 0 :
-	    WM_WIDTH_NOT_RESIZABLE|WM_HEIGHT_NOT_RESIZABLE);
-    UInt64 attributes = (wmPtr->attributes &
-	    ~macClassAttrs[macClass].forceOffAttrs) |
+	     WM_WIDTH_NOT_RESIZABLE|WM_HEIGHT_NOT_RESIZABLE);
+	UInt64 attributes = (wmPtr->attributes &
+			     ~macClassAttrs[macClass].forceOffAttrs) |
 	    macClassAttrs[macClass].forceOnAttrs;
-    NSUInteger styleMask = macClassAttrs[macClass].styleMask |
-	((attributes & kWindowNoTitleBarAttribute) ? 0 : NSTitledWindowMask) |
-	((attributes & kWindowCloseBoxAttribute) ? NSClosableWindowMask : 0) |
-	((attributes & kWindowCollapseBoxAttribute) ?
-		NSMiniaturizableWindowMask : 0) |
-	((attributes & kWindowResizableAttribute) ? NSResizableWindowMask : 0) |
-	((attributes & kWindowMetalAttribute) ?
-		NSTexturedBackgroundWindowMask : 0) |
-	((attributes & kWindowUnifiedTitleAndToolbarAttribute) ?
-		NSUnifiedTitleAndToolbarWindowMask : 0) |
-	((attributes & kWindowSideTitlebarAttribute) ? 1 << 9 : 0) |
-	(attributes >> WM_NSMASK_SHIFT);
-    Class winClass = (macClass == kDrawerWindowClass ? [TKDrawerWindow class] :
-	    (styleMask & (NSUtilityWindowMask|NSDocModalWindowMask|
-	    NSNonactivatingPanelMask|NSHUDWindowMask)) ? [TKPanel class] :
-	    [TKWindow class]);
+	styleMask = macClassAttrs[macClass].styleMask |
+	    ((attributes & kWindowNoTitleBarAttribute) ? 0 : NSTitledWindowMask) |
+	    ((attributes & kWindowCloseBoxAttribute) ? NSClosableWindowMask : 0) |
+	    ((attributes & kWindowCollapseBoxAttribute) ?
+	     NSMiniaturizableWindowMask : 0) |
+	    ((attributes & kWindowResizableAttribute) ? NSResizableWindowMask : 0) |
+	    ((attributes & kWindowMetalAttribute) ?
+	     NSTexturedBackgroundWindowMask : 0) |
+	    ((attributes & kWindowUnifiedTitleAndToolbarAttribute) ?
+	     NSUnifiedTitleAndToolbarWindowMask : 0) |
+	    ((attributes & kWindowSideTitlebarAttribute) ? 1 << 9 : 0) |
+	    (attributes >> WM_NSMASK_SHIFT);
+	winClass = (macClass == kDrawerWindowClass ? [TKDrawerWindow class] :
+		    (styleMask & (NSUtilityWindowMask|NSDocModalWindowMask|
+				  NSNonactivatingPanelMask|NSHUDWindowMask)) ?
+		    [TKPanel class] : [TKWindow class]);
+    }
     NSRect structureRect = [winClass frameRectForContentRect:NSZeroRect
 	    styleMask:styleMask];
     NSRect contentRect = NSMakeRect(5 - structureRect.origin.x,
 	    TkMacOSXZeroScreenHeight() - (TkMacOSXZeroScreenTop() + 5 +
 	    structureRect.origin.y + structureRect.size.height + 200), 200, 200);
     if (wmPtr->hints.initial_state == WithdrawnState) {
+	//// ???????
     }
     TKWindow *window = [[winClass alloc] initWithContentRect:contentRect
 	    styleMask:styleMask backing:NSBackingStoreBuffered defer:YES];
     if (!window) {
     	Tcl_Panic("couldn't allocate new Mac window");
     }
+#if MAC_OS_X_VERSION_MAX_ALLOWED > 101200
+    if (tabbingId) {
+	identifier = [NSString stringWithUTF8String:tabbingId];
+    } else {
+	identifier = [NSString stringWithUTF8String:Tk_PathName(winPtr)];
+    }
+    [window setTabbingIdentifier: identifier];
+    [window setTabbingMode: tabbingMode];
+#endif
     TKContentView *contentView = [[TKContentView alloc]
 				     initWithFrame:NSZeroRect];
     [window setContentView:contentView];
     [contentView release];
     [window setDelegate:NSApp];
@@ -6297,11 +6796,15 @@
     if (overrideRedirect) {
     	XSetWindowAttributes atts;
 
     	atts.override_redirect = True;
     	Tk_ChangeWindowAttributes((Tk_Window)winPtr, CWOverrideRedirect, &atts);
-    	ApplyContainerOverrideChanges(winPtr, NULL);
+	if ([NSApp macOSVersion] >= 101300) {
+	    window.styleMask |= NSWindowStyleMaskDocModalWindow;
+	} else {
+	    ApplyContainerOverrideChanges(winPtr, NULL);
+	}
     }
     [window display];
 }
 
 /*

Index: macosx/ttkMacOSXTheme.c
==================================================================
--- macosx/ttkMacOSXTheme.c
+++ macosx/ttkMacOSXTheme.c
@@ -260,10 +260,13 @@
 	bounds.size.height -= 4;
 	bounds.origin.y += 1;
 	break;
     case TkRecessedButton:
 	bounds.size.height -= 2;
+	break;
+    case TkSidebarButton:
+	bounds.size.height += 8;
 	break;
     case kThemeRoundButtonHelp:
 	if (isDark) {
 	    bounds.size.height = bounds.size.width = 22;
 	} else {
@@ -1202,10 +1205,13 @@
 	DrawGrayButton(context, bounds, &inlineDesign, state, tkwin);
 	break;
     case TkRecessedButton:
 	DrawGrayButton(context, bounds, &recessedDesign, state, tkwin);
 	break;
+    case TkSidebarButton:
+	DrawGrayButton(context, bounds, &sidebarDesign, state, tkwin);
+	break;
     case kThemeRoundedBevelButton:
 	DrawGrayButton(context, bounds, &bevelDesign, state, tkwin);
 	break;
     case kThemePushButton:
 
@@ -1687,10 +1693,13 @@
     CGRect contentBounds, backgroundBounds;
     int verticalPad;
 
     ButtonElementMinSize(clientData, minWidth, minHeight);
     switch (info.kind) {
+    case TkSidebarButton:
+	*paddingPtr = Ttk_MakePadding(30, 10, 30, 10);
+	return;
     case TkGradientButton:
 	*paddingPtr = Ttk_MakePadding(1, 1, 1, 1);
         /* Fall through. */
     case kThemeArrowButton:
     case kThemeRoundButtonHelp:
@@ -1767,10 +1776,11 @@
      */
 
     case kThemeArrowButton:
     case kThemeCheckBox:
     case kThemeRadioButton:
+    case TkSidebarButton:
     	break;
 
     /*
      * Other buttons have a maximum height.   We have to deal with that.
      */
@@ -3442,10 +3452,17 @@
 
 TTK_LAYOUT("RecessedButton",
     TTK_GROUP("RecessedButton.button", TTK_FILL_BOTH,
     TTK_GROUP("Button.padding", TTK_FILL_BOTH,
     TTK_NODE("Button.label", TTK_FILL_BOTH))))
+
+/* Sidebar Button - text only radio button for sidebars */
+
+TTK_LAYOUT("SidebarButton",
+    TTK_GROUP("SidebarButton.button", TTK_FILL_BOTH,
+    TTK_GROUP("Button.padding", TTK_FILL_BOTH,
+    TTK_NODE("Button.label", TTK_FILL_BOTH))))
 
 /* DisclosureButton (not a triangle) -- No label, no border*/
 TTK_LAYOUT("DisclosureButton",
     TTK_NODE("DisclosureButton.button", TTK_FILL_BOTH))
 
@@ -3579,10 +3596,12 @@
 	&ButtonElementSpec, &CheckBoxParams);
     Ttk_RegisterElementSpec(themePtr, "Radiobutton.button",
 	&ButtonElementSpec, &RadioButtonParams);
     Ttk_RegisterElementSpec(themePtr, "RecessedButton.button",
 	&ButtonElementSpec, &RecessedButtonParams);
+    Ttk_RegisterElementSpec(themePtr, "SidebarButton.button",
+	&ButtonElementSpec, &SidebarButtonParams);
     Ttk_RegisterElementSpec(themePtr, "Toolbutton.border",
 	&ButtonElementSpec, &BevelButtonParams);
     Ttk_RegisterElementSpec(themePtr, "Menubutton.button",
 	&ButtonElementSpec, &PopupButtonParams);
     Ttk_RegisterElementSpec(themePtr, "DisclosureButton.button",

Index: macosx/ttkMacOSXTheme.h
==================================================================
--- macosx/ttkMacOSXTheme.h
+++ macosx/ttkMacOSXTheme.h
@@ -299,10 +299,31 @@
       .dark =  {.face = 256.0, .top = 256.0, .side = 256.0, .bottom = 256.0},
       .onBits = 0, .offBits = 0
     }
   }
 };
+
+static const ButtonDesign sidebarDesign = {
+  .radius = 8.0,
+  .palettes = {
+    {
+      .light = {.face = 210.0, .top = 210.0, .side = 210.0, .bottom = 210.0},
+      .dark =  {.face = 129.0, .top = 129.0, .side = 129.0, .bottom = 129.0},
+      .onBits = TTK_STATE_SELECTED, .offBits = 0
+    },
+    {
+      .light = {.face = 210.0, .top = 210.0, .side = 210.0, .bottom = 210.0},
+      .dark =  {.face = 129.0, .top = 129.0, .side = 129.0, .bottom = 129.0},
+      .onBits = TTK_STATE_PRESSED, .offBits = 0
+    },
+    {
+      .light = {.face = 256.0, .top = 256.0, .side = 256.0, .bottom = 256.0},
+      .dark =  {.face = 256.0, .top = 256.0, .side = 256.0, .bottom = 256.0},
+      .onBits = 0, .offBits = 0
+    }
+  }
+};
 
 static const ButtonDesign incdecDesign = {
   .radius = 5.0,
   .palettes = {
     {
@@ -472,10 +493,11 @@
 
 #define TkGradientButton    0x8001
 #define TkRoundedRectButton 0x8002
 #define TkRecessedButton    0x8003
 #define TkInlineButton      0x8004
+#define TkSidebarButton     0x8005
 /*
  * The struct passed as clientData when drawing Ttk buttons.
  */
 
 typedef struct {
@@ -507,12 +529,12 @@
     GradientButtonParams = {TkGradientButton, NoThemeMetric, NoThemeMetric},
     RoundedRectButtonParams = {TkRoundedRectButton, kThemeMetricPushButtonHeight,
 			       NoThemeMetric},
     RecessedButtonParams = {TkRecessedButton, kThemeMetricPushButtonHeight,
  			    NoThemeMetric},
-    InlineButtonParams = {TkInlineButton,  kThemeMetricPushButtonHeight,
-  			  NoThemeMetric};
+    SidebarButtonParams = {TkSidebarButton, NoThemeMetric, NoThemeMetric},
+    InlineButtonParams = {TkInlineButton,  kThemeMetricPushButtonHeight, NoThemeMetric};
 
     /*
      * Others: kThemeDisclosureRight, kThemeDisclosureDown,
      * kThemeDisclosureLeft
      */

Index: tests/event.test
==================================================================
--- tests/event.test
+++ tests/event.test
@@ -854,18 +854,21 @@
     wm geometry . 200x200+300+300
     wm deiconify .
     _pause 200
     toplevel .top2 -width 200 -height 200
     wm geometry .top2 +[expr {[winfo rootx .]+50}]+[expr {[winfo rooty .]+50}]
+    update idletasks
     wm deiconify .top2
+    update idletasks
     raise .top2
     _pause 400
     event generate .top2 <Motion> -warp 1 -x 50 -y 50
     _pause 100
     bind . <Enter> {lappend res %W}
     set res [list ]
     destroy .top2
+    update idletasks
     _pause 200
     set res
 } -cleanup {
     deleteWindows
     bind . <Enter> $EnterBind
@@ -882,11 +885,13 @@
     wm geometry .top1 200x200+300+300
     wm deiconify .top1
     _pause 200
     toplevel .top2 -width 200 -height 200
     wm geometry .top2 +[expr {[winfo rootx .top1]+50}]+[expr {[winfo rooty .top1]+50}]
+    update idletasks
     wm deiconify .top2
+    update idletasks
     raise .top2
     _pause 400
     event generate .top2 <Motion> -warp 1 -x 50 -y 50
     _pause 100
     bind .top1 <Enter> {lappend res %W}

Index: tests/unixWm.test
==================================================================
--- tests/unixWm.test
+++ tests/unixWm.test
@@ -2065,11 +2065,13 @@
     list $result [winfo containing [winfo rootx .raise2] \
 	    [winfo rooty .raise2]]
 } {.raise1 .raise3}
 deleteWindows
 test unixWm-51.6 {TkWmRestackToplevel procedure, window to be stacked isn't mapped} unix {
+    wm geometry . +300+300
     destroy .t
+    update idletasks
     toplevel .t -width 200 -height 200 -bg green
     tkwait visibility .t
     wm geometry .t +0+0
     update
     restackDelay
@@ -2528,13 +2530,11 @@
 #
 # NOTE: since [wm attributes] is not guaranteed to have any effect,
 # the only thing we can really test here is the syntax.
 #
 if {[tk windowingsystem] eq "aqua"} {
-    set result_60_1 {-alpha 1.0 -fullscreen 0 -modified 0 -notify 0\
-			 -titlepath {} -topmost 0 -transparent 0\
-			 -type unsupported}
+    set result_60_1 {-alpha 1.0 -appearance auto -buttons {close miniaturize zoom} -fullscreen 0 -isdark 0 -modified 0 -notify 0 -titlepath {} -topmost 0 -transparent 0 -stylemask {titled closable miniaturizable resizable} -class nswindow -tabbingid .t -tabbingmode auto -type unsupported}
 } else {
     set result_60_1 {-alpha 1.0 -fullscreen 0 -topmost 0 -type {} -zoomed 0}
 }
 test unixWm-60.1 {wm attributes - test} -constraints unix -body {
     destroy .t

Index: tests/wm.test
==================================================================
--- tests/wm.test
+++ tests/wm.test
@@ -202,14 +202,16 @@
     wm attributes . -to
 } -result {bad attribute "-to": must be -alpha, -disabled, -fullscreen, -toolwindow, -topmost, or -transparentcolor}
 test wm-attributes-1.2.4 {usage} -constraints {unix notAqua} -returnCodes error -body {
     wm attributes . _
 } -result {bad attribute "_": must be -alpha, -fullscreen, -topmost, -type, or -zoomed}
+if {[tk windowingsystem] eq "aqua"} {
+    set result_1_2_5 {bad attribute "_": must be -alpha, -appearance, -buttons, -fullscreen, -isdark, -modified, -notify, -titlepath, -topmost, -transparent, -stylemask, -class, -tabbingid, -tabbingmode, or -type}
+} else {set result_1_2_5 {bad attribute "_": must be -alpha, -fullscreen, -modified, -notify, -titlepath, -topmost, -transparent, or -type}}
 test wm-attributes-1.2.5 {usage} -constraints aqua -returnCodes error -body {
     wm attributes . _
-} -result {bad attribute "_": must be -alpha, -fullscreen, -modified, -notify, -titlepath, -topmost, -transparent, or -type}
-
+} -result $result_1_2_5
 
 ### wm client ###
 test wm-client-1.1 {usage} -returnCodes error -body {
     wm client
 } -result {wrong # args: should be "wm option window ?arg ...?"}