Add support for a single "marked pane". There is one marked pane in the

server at a time; it may be toggled or cleared with select-pane -m and
-M (the border is highlighted). A new target '~' or '{marked}' specifies
the marked pane to commands and it is the default target for the
swap-pane and join-pane -s flag (this makes them much simpler to use -
mark the source pane and then change to the target pane to run swapp or
joinp).

11 files changed, 296 insertions, 40 deletions

diff --git a/cmd-find.c b/cmd-find.c
index 98f1e187..2b862f95 100644
--- a/cmd-find.c
+++ b/cmd-find.c
@@ -29,6 +29,7 @@
 #define CMD_FIND_PREFER_UNATTACHED 0x1
 #define CMD_FIND_QUIET 0x2
 #define CMD_FIND_WINDOW_INDEX 0x4
+#define CMD_FIND_DEFAULT_MARKED 0x8
 
 enum cmd_find_type {
 	CMD_FIND_PANE,
@@ -759,7 +760,14 @@ cmd_find_target(struct cmd_q *cmdq, const char *target, enum cmd_find_type type,
 
 	/* Find current state. */
 	cmd_find_clear_state(&current, cmdq, flags);
-	if (cmd_find_current_session(&current) != 0) {
+	if (server_check_marked() && (flags & CMD_FIND_DEFAULT_MARKED)) {
+		current.s = marked_session;
+		current.wl = marked_winlink;
+		current.idx = current.wl->idx;
+		current.w = current.wl->window;
+		current.wp = marked_window_pane;
+	}
+	if (current.s == NULL && cmd_find_current_session(&current) != 0) {
 		if (~flags & CMD_FIND_QUIET)
 			cmdq_error(cmdq, "no current session");
 		goto error;
@@ -798,9 +806,24 @@ cmd_find_target(struct cmd_q *cmdq, const char *target, enum cmd_find_type type,
 		}
 		return (&fs);
 	}
-	copy = xstrdup(target);
+
+	/* Marked target is a plain ~ or {marked}. */
+	if (strcmp(target, "~") == 0 || strcmp(target, "{marked}") == 0) {
+		if (!server_check_marked()) {
+			if (~flags & CMD_FIND_QUIET)
+				cmdq_error(cmdq, "no marked target");
+			goto error;
+		}
+		fs.s = marked_session;
+		fs.wl = marked_winlink;
+		fs.idx = fs.wl->idx;
+		fs.w = fs.wl->window;
+		fs.wp = marked_window_pane;
+		return (&fs);
+	}
 
 	/* Find separators if they exist. */
+	copy = xstrdup(target);
 	colon = strchr(copy, ':');
 	if (colon != NULL)
 		*colon++ = '\0';
@@ -1053,6 +1076,24 @@ cmd_find_window(struct cmd_q *cmdq, const char *target, struct session **sp)
 	return (fs->wl);
 }
 
+/* Find the target window, defaulting to marked rather than current. */
+struct winlink *
+cmd_find_window_marked(struct cmd_q *cmdq, const char *target,
+    struct session **sp)
+{
+	struct cmd_find_state	*fs;
+	int			 flags = CMD_FIND_DEFAULT_MARKED;
+
+	fs = cmd_find_target(cmdq, target, CMD_FIND_WINDOW, flags);
+	cmd_find_log_state(__func__, target, fs);
+	if (fs == NULL)
+		return (NULL);
+
+	if (sp != NULL)
+		*sp = fs->s;
+	return (fs->wl);
+}
+
 /* Find the target pane and report an error and return NULL. */
 struct winlink *
 cmd_find_pane(struct cmd_q *cmdq, const char *target, struct session **sp,
@@ -1072,6 +1113,26 @@ cmd_find_pane(struct cmd_q *cmdq, const char *target, struct session **sp,
 	return (fs->wl);
 }
 
+/* Find the target pane, defaulting to marked rather than current. */
+struct winlink *
+cmd_find_pane_marked(struct cmd_q *cmdq, const char *target,
+    struct session **sp, struct window_pane **wpp)
+{
+	struct cmd_find_state	*fs;
+	int			 flags = CMD_FIND_DEFAULT_MARKED;
+
+	fs = cmd_find_target(cmdq, target, CMD_FIND_PANE, flags);
+	cmd_find_log_state(__func__, target, fs);
+	if (fs == NULL)
+		return (NULL);
+
+	if (sp != NULL)
+		*sp = fs->s;
+	if (wpp != NULL)
+		*wpp = fs->wp;
+	return (fs->wl);
+}
+
 /* Find the target client or report an error and return NULL. */
 struct client *
 cmd_find_client(struct cmd_q *cmdq, const char *target, int quiet)
diff --git a/cmd-join-pane.c b/cmd-join-pane.c
index 943cdce4..b995b674 100644
--- a/cmd-join-pane.c
+++ b/cmd-join-pane.c
@@ -75,7 +75,7 @@ join_pane(struct cmd *self, struct cmd_q *cmdq, int not_same_window)
 	dst_idx = dst_wl->idx;
 	server_unzoom_window(dst_w);
 
-	src_wl = cmd_find_pane(cmdq, args_get(args, 's'), NULL, &src_wp);
+	src_wl = cmd_find_pane_marked(cmdq, args_get(args, 's'), NULL, &src_wp);
 	if (src_wl == NULL)
 		return (CMD_RETURN_ERROR);
 	src_w = src_wl->window;
diff --git a/cmd-select-pane.c b/cmd-select-pane.c
index f237e8fd..5ea4bdc3 100644
--- a/cmd-select-pane.c
+++ b/cmd-select-pane.c
@@ -28,8 +28,8 @@ enum cmd_retval	 cmd_select_pane_exec(struct cmd *, struct cmd_q *);
 
 const struct cmd_entry cmd_select_pane_entry = {
 	"select-pane", "selectp",
-	"DdegLlP:Rt:U", 0, 0,
-	"[-DdegLlRU] [-P style] " CMD_TARGET_PANE_USAGE,
+	"DdegLlMmP:Rt:U", 0, 0,
+	"[-DdegLlMmRU] [-P style] " CMD_TARGET_PANE_USAGE,
 	0,
 	cmd_select_pane_exec
 };
@@ -47,7 +47,8 @@ cmd_select_pane_exec(struct cmd *self, struct cmd_q *cmdq)
 {
 	struct args		*args = self->args;
 	struct winlink		*wl;
-	struct window_pane	*wp;
+	struct session		*s;
+	struct window_pane	*wp, *lastwp, *markedwp;
 	const char		*style;
 
 	if (self->entry == &cmd_last_pane_entry || args_has(args, 'l')) {
@@ -74,9 +75,31 @@ cmd_select_pane_exec(struct cmd *self, struct cmd_q *cmdq)
 		return (CMD_RETURN_NORMAL);
 	}
 
-	if ((wl = cmd_find_pane(cmdq, args_get(args, 't'), NULL, &wp)) == NULL)
+	if ((wl = cmd_find_pane(cmdq, args_get(args, 't'), &s, &wp)) == NULL)
 		return (CMD_RETURN_ERROR);
 
+	if (args_has(args, 'm') || args_has(args, 'M')) {
+		if (args_has(args, 'm') && !window_pane_visible(wp))
+			return (CMD_RETURN_NORMAL);
+		lastwp = marked_window_pane;
+
+		if (args_has(args, 'M') || server_is_marked(s, wl, wp))
+			server_clear_marked();
+		else
+			server_set_marked(s, wl, wp);
+		markedwp = marked_window_pane;
+
+		if (lastwp != NULL) {
+			server_redraw_window_borders(lastwp->window);
+			server_status_window(lastwp->window);
+		}
+		if (markedwp != NULL) {
+			server_redraw_window_borders(markedwp->window);
+			server_status_window(markedwp->window);
+		}
+		return (CMD_RETURN_NORMAL);
+	}
+
 	if (args_has(self->args, 'P') || args_has(self->args, 'g')) {
 		if (args_has(args, 'P')) {
 			style = args_get(args, 'P');
diff --git a/cmd-swap-pane.c b/cmd-swap-pane.c
index 918a2e4f..c4751c36 100644
--- a/cmd-swap-pane.c
+++ b/cmd-swap-pane.c
@@ -58,18 +58,22 @@ cmd_swap_pane_exec(struct cmd *self, struct cmd_q *cmdq)
 			src_wp = TAILQ_NEXT(dst_wp, entry);
 			if (src_wp == NULL)
 				src_wp = TAILQ_FIRST(&dst_w->panes);
+			src_wl = dst_wl;
 		} else if (args_has(self->args, 'U')) {
 			src_wp = TAILQ_PREV(dst_wp, window_panes, entry);
 			if (src_wp == NULL)
 				src_wp = TAILQ_LAST(&dst_w->panes, window_panes);
+			src_wl = dst_wl;
 		} else {
-			src_wl = cmd_find_pane(cmdq, NULL, NULL, &src_wp);
+			src_wl = cmd_find_pane_marked(cmdq, NULL, NULL,
+			    &src_wp);
 			if (src_wl == NULL)
 				return (CMD_RETURN_ERROR);
 			src_w = src_wl->window;
 		}
 	} else {
-		src_wl = cmd_find_pane(cmdq, args_get(args, 's'), NULL, &src_wp);
+		src_wl = cmd_find_pane_marked(cmdq, args_get(args, 's'), NULL,
+		    &src_wp);
 		if (src_wl == NULL)
 			return (CMD_RETURN_ERROR);
 		src_w = src_wl->window;
diff --git a/cmd-swap-window.c b/cmd-swap-window.c
index 655b910c..51682e37 100644
--- a/cmd-swap-window.c
+++ b/cmd-swap-window.c
@@ -47,7 +47,7 @@ cmd_swap_window_exec(struct cmd *self, struct cmd_q *cmdq)
 	struct window		*w;
 
 	target_src = args_get(args, 's');
-	if ((wl_src = cmd_find_window(cmdq, target_src, &src)) == NULL)
+	if ((wl_src = cmd_find_window_marked(cmdq, target_src, &src)) == NULL)
 		return (CMD_RETURN_ERROR);
 	target_dst = args_get(args, 't');
 	if ((wl_dst = cmd_find_window(cmdq, target_dst, &dst)) == NULL)
diff --git a/key-bindings.c b/key-bindings.c
index a3cb0bea..ab4751f9 100644
--- a/key-bindings.c
+++ b/key-bindings.c
@@ -177,6 +177,7 @@ key_bindings_init(void)
 		"bind ? list-keys",
 		"bind D choose-client",
 		"bind L switch-client -l",
+		"bind M select-pane -M",
 		"bind [ copy-mode",
 		"bind ] paste-buffer",
 		"bind c new-window",
@@ -184,6 +185,7 @@ key_bindings_init(void)
 		"bind f command-prompt \"find-window '%%'\"",
 		"bind i display-message",
 		"bind l last-window",
+		"bind m select-pane -m",
 		"bind n next-window",
 		"bind o select-pane -t:.+",
 		"bind p previous-window",
@@ -222,6 +224,7 @@ key_bindings_init(void)
 		"bind -n MouseDrag1Border resize-pane -M",
 		"bind -n MouseDown1Status select-window -t=",
 		"bind -n MouseDrag1Pane if -Ft= '#{mouse_any_flag}' 'if -Ft= \"#{pane_in_mode}\" \"copy-mode -M\" \"send-keys -M\"' 'copy-mode -M'",
+		"bind -n MouseDown3Pane select-pane -mt=",
 	};
 	u_int		 i;
 	struct cmd_list	*cmdlist;
diff --git a/screen-redraw.c b/screen-redraw.c
index babc74a9..799f5c55 100644
--- a/screen-redraw.c
+++ b/screen-redraw.c
@@ -26,8 +26,8 @@ int	screen_redraw_cell_border1(struct window_pane *, u_int, u_int);
 int	screen_redraw_cell_border(struct client *, u_int, u_int);
 int	screen_redraw_check_cell(struct client *, u_int, u_int,
 	    struct window_pane **);
-int	screen_redraw_check_active(u_int, u_int, int, struct window *,
-	    struct window_pane *);
+int	screen_redraw_check_is(u_int, u_int, int, struct window *,
+	    struct window_pane *, struct window_pane *);
 
 void	screen_redraw_draw_borders(struct client *, int, u_int);
 void	screen_redraw_draw_panes(struct client *, u_int);
@@ -175,13 +175,13 @@ screen_redraw_check_cell(struct client *c, u_int px, u_int py,
 	return (CELL_OUTSIDE);
 }
 
-/* Check active pane indicator. */
+/* Check if the border of a particular pane. */
 int
-screen_redraw_check_active(u_int px, u_int py, int type, struct window *w,
-    struct window_pane *wp)
+screen_redraw_check_is(u_int px, u_int py, int type, struct window *w,
+    struct window_pane *wantwp, struct window_pane *wp)
 {
 	/* Is this off the active pane border? */
-	if (screen_redraw_cell_border1(w->active, px, py) != 1)
+	if (screen_redraw_cell_border1(wantwp, px, py) != 1)
 		return (0);
 
 	/* If there are more than two panes, that's enough. */
@@ -196,7 +196,7 @@ screen_redraw_check_active(u_int px, u_int py, int type, struct window *w,
 	if (wp->xoff == 0 && wp->sx == w->sx) {
 		/* This can either be the top pane or the bottom pane. */
 		if (wp->yoff == 0) { /* top pane */
-			if (wp == w->active)
+			if (wp == wantwp)
 				return (px <= wp->sx / 2);
 			return (px > wp->sx / 2);
 		}
@@ -207,7 +207,7 @@ screen_redraw_check_active(u_int px, u_int py, int type, struct window *w,
 	if (wp->yoff == 0 && wp->sy == w->sy) {
 		/* This can either be the left pane or the right pane. */
 		if (wp->xoff == 0) { /* left pane */
-			if (wp == w->active)
+			if (wp == wantwp)
 				return (py <= wp->sy / 2);
 			return (py > wp->sy / 2);
 		}
@@ -274,13 +274,15 @@ screen_redraw_pane(struct client *c, struct window_pane *wp)
 void
 screen_redraw_draw_borders(struct client *c, int status, u_int top)
 {
-	struct window		*w = c->session->curw->window;
+	struct session		*s = c->session;
+	struct window		*w = s->curw->window;
 	struct options		*oo = &w->options;
 	struct tty		*tty = &c->tty;
 	struct window_pane	*wp;
-	struct grid_cell	 active_gc, other_gc, msg_gc;
+	struct grid_cell	 m_active_gc, active_gc, m_other_gc, other_gc;
+	struct grid_cell	 msg_gc;
 	u_int		 	 i, j, type, msgx = 0, msgy = 0;
-	int			 small, flags;
+	int			 active, small, flags;
 	char			 msg[256];
 	const char		*tmp;
 	size_t			 msglen = 0;
@@ -314,15 +316,29 @@ screen_redraw_draw_borders(struct client *c, int status, u_int top)
 	style_apply(&active_gc, oo, "pane-active-border-style");
 	active_gc.attr = other_gc.attr = GRID_ATTR_CHARSET;
 
+	memcpy(&m_other_gc, &other_gc, sizeof m_other_gc);
+	m_other_gc.attr ^= GRID_ATTR_REVERSE;
+	memcpy(&m_active_gc, &active_gc, sizeof m_active_gc);
+	m_active_gc.attr ^= GRID_ATTR_REVERSE;
+
 	for (j = 0; j < tty->sy - status; j++) {
 		for (i = 0; i < tty->sx; i++) {
 			type = screen_redraw_check_cell(c, i, j, &wp);
 			if (type == CELL_INSIDE)
 				continue;
-			if (type == CELL_OUTSIDE &&
-			    small && i > msgx && j == msgy)
+			if (type == CELL_OUTSIDE && small &&
+			    i > msgx && j == msgy)
 				continue;
-			if (screen_redraw_check_active(i, j, type, w, wp))
+			active = screen_redraw_check_is(i, j, type, w,
+			    w->active, wp);
+			if (server_is_marked(s, s->curw, marked_window_pane) &&
+			    screen_redraw_check_is(i, j, type, w,
+			    marked_window_pane, wp)) {
+				if (active)
+					tty_attributes(tty, &m_active_gc, NULL);
+				else
+					tty_attributes(tty, &m_other_gc, NULL);
+			} else if (active)
 				tty_attributes(tty, &active_gc, NULL);
 			else
 				tty_attributes(tty, &other_gc, NULL);
diff --git a/server.c b/server.c
index b53648f0..52fdb0c3 100644
--- a/server.c
+++ b/server.c
@@ -50,19 +50,85 @@ int		 server_shutdown;
 struct event	 server_ev_accept;
 struct event	 server_ev_second;
 
-int		 server_create_socket(void);
-void		 server_loop(void);
-int		 server_should_shutdown(void);
-void		 server_send_shutdown(void);
-void		 server_clean_dead(void);
-void		 server_accept_callback(int, short, void *);
-void		 server_signal_callback(int, short, void *);
-void		 server_child_signal(void);
-void		 server_child_exited(pid_t, int);
-void		 server_child_stopped(pid_t, int);
-void		 server_second_callback(int, short, void *);
-void		 server_lock_server(void);
-void		 server_lock_sessions(void);
+struct session		*marked_session;
+struct winlink		*marked_winlink;
+struct window		*marked_window;
+struct window_pane	*marked_window_pane;
+struct layout_cell	*marked_layout_cell;
+
+int	server_create_socket(void);
+void	server_loop(void);
+int	server_should_shutdown(void);
+void	server_send_shutdown(void);
+void	server_clean_dead(void);
+void	server_accept_callback(int, short, void *);
+void	server_signal_callback(int, short, void *);
+void	server_child_signal(void);
+void	server_child_exited(pid_t, int);
+void	server_child_stopped(pid_t, int);
+void	server_second_callback(int, short, void *);
+void	server_lock_server(void);
+void	server_lock_sessions(void);
+
+/* Set marked pane. */
+void
+server_set_marked(struct session *s, struct winlink *wl, struct window_pane *wp)
+{
+	marked_session = s;
+	marked_winlink = wl;
+	marked_window = wl->window;
+	marked_window_pane = wp;
+	marked_layout_cell = wp->layout_cell;
+}
+
+/* Clear marked pane. */
+void
+server_clear_marked(void)
+{
+	marked_session = NULL;
+	marked_winlink = NULL;
+	marked_window = NULL;
+	marked_window_pane = NULL;
+	marked_layout_cell = NULL;
+}
+
+/* Is this the marked pane? */
+int
+server_is_marked(struct session *s, struct winlink *wl, struct window_pane *wp)
+{
+	if (s == NULL || wl == NULL || wp == NULL)
+		return (0);
+	if (marked_session != s || marked_winlink != wl)
+		return (0);
+	if (marked_window_pane != wp)
+		return (0);
+	return (server_check_marked());
+}
+
+/* Check if the marked pane is still valid. */
+int
+server_check_marked(void)
+{
+	struct winlink	*wl;
+
+	if (marked_window_pane == NULL)
+		return (0);
+	if (marked_layout_cell != marked_window_pane->layout_cell)
+		return (0);
+
+	if (!session_alive(marked_session))
+		return (0);
+	RB_FOREACH(wl, winlinks, &marked_session->windows) {
+		if (wl->window == marked_window && wl == marked_winlink)
+			break;
+	}
+	if (wl == NULL)
+		return (0);
+
+	if (!window_has_pane(marked_window, marked_window_pane))
+		return (0);
+	return (window_pane_visible(marked_window_pane));
+}
 
 /* Create server socket. */
 int
diff --git a/tmux.1 b/tmux.1
index 1233d1be..015e5ee7 100644
--- a/tmux.1
+++ b/tmux.1
@@ -298,6 +298,12 @@ Change to the previous window.
 Briefly display pane indexes.
 .It r
 Force redraw of the attached client.
+.It m
+Mark the current pane (see
+.Ic select-pane
+.Fl m ) .
+.It M
+Clear the marked pane.
 .It s
 Select a new session for the attached client interactively.
 .It t
@@ -351,6 +357,8 @@ This section contains a list of the commands supported by
 .Nm .
 Most commands accept the optional
 .Fl t
+(and sometimes
+.Fl s )
 argument with one of
 .Ar target-client ,
 .Ar target-session
@@ -451,7 +459,6 @@ Each has a single-character alternative form.
 .It Li "{last}" Ta "!" Ta "The last (previously current) window"
 .It Li "{next}" Ta "+" Ta "The next window by number"
 .It Li "{previous}" Ta "-" Ta "The previous window by number"
-.It Li "{mouse}" Ta "=" Ta "The window where the mouse event happened"
 .El
 .Pp
 .Ar target-pane
@@ -481,7 +488,6 @@ The following special tokens are available for the pane index:
 .It Li "{down}" Ta "" Ta "The pane below the active pane"
 .It Li "{left}" Ta "" Ta "The pane to the left of the active pane"
 .It Li "{right}" Ta "" Ta "The pane to the right of the active pane"
-.It Li "{mouse}" Ta "=" Ta "The pane where the mouse event happened"
 .El
 .Pp
 The tokens
@@ -493,6 +499,27 @@ may be followed by an offset, for example:
 select-window -t:+2
 .Ed
 .Pp
+In addition,
+.Em target-session ,
+.Em target-window
+or
+.Em target-pane
+may consist entirely of the token
+.Ql {mouse}
+(alternative form
+.Ql = )
+to specify the most recent mouse event
+(see the
+.Sx MOUSE SUPPORT
+section)
+or
+.Ql {marked}
+(alternative form
+.Ql ~ )
+to specify the marked pane (see
+.Ic select-pane
+.Fl m ) .
+.Pp
 Sessions, window and panes are each numbered with a unique ID; session IDs are
 prefixed with a
 .Ql $ ,
@@ -1440,6 +1467,13 @@ option causes
 .Ar src-pane
 to be joined to left of or above
 .Ar dst-pane .
+.Pp
+If
+.Fl s
+is omitted and a marked pane is present (see
+.Ic select-pane
+.Fl m ) ,
+the marked pane is used rather than the current pane.
 .It Xo Ic kill-pane
 .Op Fl a
 .Op Fl t Ar target-pane
@@ -1795,7 +1829,7 @@ commands.
 .Fl o
 applies the last set layout if possible (undoes the most recent layout change).
 .It Xo Ic select-pane
-.Op Fl DdegLlRU
+.Op Fl DdegLlMmRU
 .Op Fl P Ar style
 .Op Fl t Ar target-pane
 .Xc
@@ -1823,6 +1857,20 @@ enables or
 .Fl d
 disables input to the pane.
 .Pp
+.Fl m
+and
+.Fl M
+are used to set and clear the
+.Em marked pane .
+There is one marked pane at a time, setting a new marked pane clears the last.
+The marked pane is the default target for
+.Fl s
+to
+.Ic join-pane ,
+.Ic swap-pane
+and
+.Ic swap-window .
+.Pp
 Each pane has a style: by default the
 .Ic window-style
 and
@@ -1911,6 +1959,13 @@ swaps with the next pane (after it numerically).
 instructs
 .Nm
 not to change the active pane.
+.Pp
+If
+.Fl s
+is omitted and a marked pane is present (see
+.Ic select-pane
+.Fl m ) ,
+the marked pane is used rather than the current pane.
 .It Xo Ic swap-window
 .Op Fl d
 .Op Fl s Ar src-window
@@ -1922,6 +1977,15 @@ This is similar to
 except the source and destination windows are swapped.
 It is an error if no window exists at
 .Ar src-window .
+.Pp
+Like
+.Ic swap-pane ,
+if
+.Fl s
+is omitted and a marked pane is present (see
+.Ic select-pane
+.Fl m ) ,
+the window containing the marked pane is used rather than the current window.
 .It Xo Ic unlink-window
 .Op Fl k
 .Op Fl t Ar target-window
@@ -3488,6 +3552,7 @@ The flag is one of the following symbols appended to the window name:
 .It Li "#" Ta "Window is monitored and activity has been detected."
 .It Li "!" Ta "A bell has occurred in the window."
 .It Li "~" Ta "The window has been silent for the monitor-silence interval."
+.It Li "M" Ta "The window contains the marked pane."
 .It Li "Z" Ta "The window's active pane is zoomed."
 .El
 .Pp
diff --git a/tmux.h b/tmux.h
index 78e64170..ae1682af 100644
--- a/tmux.h
+++ b/tmux.h
@@ -1688,8 +1688,12 @@ struct session	*cmd_find_current(struct cmd_q *);
 struct session	*cmd_find_session(struct cmd_q *, const char *, int);
 struct winlink	*cmd_find_window(struct cmd_q *, const char *,
 		     struct session **);
+struct winlink	*cmd_find_window_marked(struct cmd_q *, const char *,
+		     struct session **);
 struct winlink	*cmd_find_pane(struct cmd_q *, const char *, struct session **,
 		     struct window_pane **);
+struct winlink	*cmd_find_pane_marked(struct cmd_q *, const char *,
+		     struct session **, struct window_pane **);
 struct client	*cmd_find_client(struct cmd_q *, const char *, int);
 int		 cmd_find_index(struct cmd_q *, const char *,
 		     struct session **);
@@ -1850,6 +1854,15 @@ const char *key_string_lookup_key(int);
 /* server.c */
 extern struct clients clients;
 extern struct clients dead_clients;
+extern struct session *marked_session;
+extern struct winlink *marked_winlink;
+extern struct window_pane *marked_window_pane;
+void	 server_set_marked(struct session *, struct winlink *,
+	     struct window_pane *);
+void	 server_clear_marked(void);
+int	 server_is_marked(struct session *, struct winlink *,
+	     struct window_pane *);
+int	 server_check_marked(void);
 int	 server_start(int, char *);
 void	 server_update_socket(void);
 void	 server_add_accept(int);
diff --git a/window.c b/window.c
index bc17656d..a1d6792b 100644
--- a/window.c
+++ b/window.c
@@ -543,6 +543,9 @@ window_add_pane(struct window *w, u_int hlimit)
 void
 window_lost_pane(struct window *w, struct window_pane *wp)
 {
+	if (wp == marked_window_pane)
+		server_clear_marked();
+
 	if (wp == w->active) {
 		w->active = w->last;
 		w->last = NULL;
@@ -661,6 +664,8 @@ window_printable_flags(struct session *s, struct winlink *wl)
 		flags[pos++] = '*';
 	if (wl == TAILQ_FIRST(&s->lastw))
 		flags[pos++] = '-';
+	if (server_check_marked() && wl == marked_winlink)
+		flags[pos++] = 'M';
 	if (wl->window->flags & WINDOW_ZOOMED)
 		flags[pos++] = 'Z';
 	flags[pos] = '\0';