diff --git a/regress/side-status-clamp.sh b/regress/side-status-clamp.sh
new file mode 100644
index 000000000..59687f85b
--- /dev/null
+++ b/regress/side-status-clamp.sh
@@ -0,0 +1,143 @@
+#!/bin/sh
+
+# With side-status left, a client narrower than the window must clamp pane
+# output to its visible part without killing the server or drawing over the
+# side status line. Each inner client runs in an outer pane of its size.
+
+PATH=/bin:/usr/bin
+TERM=screen
+LC_ALL=C.UTF-8
+export PATH TERM LC_ALL
+
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+TMUX="$TEST_TMUX -LtestA$$ -f/dev/null"
+TMUX2="$TEST_TMUX -LtestB$$ -f/dev/null"
+
+DIR=$(mktemp -d) || exit 1
+TRIGGER=$DIR/trigger
+CAPTURE=$DIR/capture
+
+cleanup()
+{
+	$TMUX2 kill-server >/dev/null 2>&1
+	$TMUX kill-server >/dev/null 2>&1
+	rm -f "$TRIGGER" "$CAPTURE"
+	rmdir "$DIR"
+}
+trap cleanup 0 1 15
+
+fail()
+{
+	echo "$*" >&2
+	[ -s "$CAPTURE" ] && cat "$CAPTURE" >&2
+	exit 1
+}
+
+# Start the inner server with one pane running $1, then attach a big and a
+# small client from outer panes of sizes $2 and $3 (WxH).
+start()
+{
+	$TMUX kill-server >/dev/null 2>&1
+	$TMUX2 kill-server >/dev/null 2>&1
+	rm -f "$TRIGGER"
+
+	$TMUX new-session -d -s inner -x 200 -y 50 "$1" || exit 1
+	$TMUX set -g status off || exit 1
+	$TMUX set -g automatic-rename off || exit 1
+	$TMUX set -g window-size largest || exit 1
+	$TMUX set -g side-status left || exit 1
+}
+attach()
+{
+	$TMUX2 new-session -d -s big -x "${1%x*}" -y "${1#*x}" 'sleep 100' ||
+	    exit 1
+	$TMUX2 set -g status off || exit 1
+	$TMUX2 set -g window-size manual || exit 1
+	$TMUX2 new-session -d -s small -x "${2%x*}" -y "${2#*x}" 'sleep 100' ||
+	    exit 1
+	$TMUX2 respawn-pane -k -t big:0.0 "$TMUX attach -t inner" || exit 1
+	sleep 0.5
+	$TMUX2 respawn-pane -k -t small:0.0 "$TMUX attach -t inner" || exit 1
+	sleep 1
+	$TMUX has-session 2>/dev/null || fail "server exited on attach"
+	SMALL=$($TMUX list-clients -F '#{client_width} #{client_name}' |
+	    sort -n | head -n 1 | cut -d' ' -f2)
+}
+alive()
+{
+	$TMUX has-session 2>/dev/null || fail "server exited: $1"
+}
+
+# A clear below the cursor in a pane wider than the small client's view.
+start "sh -c 'while [ ! -e $TRIGGER ]; do sleep 0.1; done
+	printf \"\\033[J\"; exec sleep 100'"
+$TMUX set -g side-status-width 31 || exit 1
+attach 167x49 40x12
+: >"$TRIGGER"
+sleep 1
+alive "clear in a pane wider than the client"
+
+# The same clear with the small client panned right, so the pane is cut off
+# on both sides. The side status line keeps the window on its first row.
+start "sh -c 'while [ ! -e $TRIGGER ]; do sleep 0.1; done
+	printf \"\\033[J\"; exec sleep 100'"
+$TMUX rename-window -t inner:0 work || exit 1
+$TMUX set -g side-status-width 31 || exit 1
+attach 167x49 40x12
+$TMUX refresh-client -t "$SMALL" -R 5 || exit 1
+sleep 0.5
+: >"$TRIGGER"
+sleep 1
+alive "clear in a pane cut off on both sides"
+$TMUX2 capture-pane -p -t small:0.0 >"$CAPTURE" || exit 1
+case "$(head -n 1 "$CAPTURE")" in
+0:work*) ;;
+*) fail "side status first row cleared" ;;
+esac
+
+# Output in the right pane of a split, cut off on the right.
+start 'sleep 100'
+$TMUX split-window -h -d "sh -c 'while [ ! -e $TRIGGER ]; do sleep 0.1; done
+	printf ab; exec sleep 100'" || exit 1
+attach 120x30 80x30
+: >"$TRIGGER"
+sleep 1
+alive "output in a pane cut off on the right"
+
+# Panned right by less than the side status width, the left pane is cut off
+# on the left. Its output is drawn after the side status line, not over it.
+start "sh -c 'while [ ! -e $TRIGGER ]; do sleep 0.1; done
+	printf \"%053d\" 0 | tr 0 X; exec sleep 100'"
+$TMUX split-window -h -d 'sleep 100' || exit 1
+attach 120x30 80x30
+$TMUX refresh-client -t "$SMALL" -R 10 || exit 1
+sleep 0.5
+: >"$TRIGGER"
+sleep 1
+alive "output in a pane cut off on the left"
+$TMUX2 capture-pane -p -t small:0.0 >"$CAPTURE" || exit 1
+row=$(head -n 1 "$CAPTURE")
+case "$row" in
+?????????????│XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX│*) ;;
+*) fail "row is '$row', expected the side status then 43 X" ;;
+esac
+
+# Panned into the middle of the right pane, which is cut off on both sides.
+# The visible columns of the pane are drawn, counted from the pane's left.
+start 'sleep 100'
+$TMUX split-window -h -d -l 100 "sh -c 'while [ ! -e $TRIGGER ]; do sleep 0.1; done
+	printf \"%010d\" 0 | sed s/0/0123456789/g; exec sleep 100'" || exit 1
+attach 214x30 40x30
+$TMUX refresh-client -t "$SMALL" -R 120 || exit 1
+sleep 0.5
+: >"$TRIGGER"
+sleep 1
+alive "output in a pane cut off on both sides"
+$TMUX2 capture-pane -p -t small:0.0 >"$CAPTURE" || exit 1
+row=$(head -n 1 "$CAPTURE")
+case "$row" in
+?????????????│01234567890123456789012345) ;;
+*) fail "row is '$row', expected the side status then pane columns 20-45" ;;
+esac
+
+exit 0
diff --git a/regress/side-status-click.sh b/regress/side-status-click.sh
new file mode 100644
index 000000000..d69c1740f
--- /dev/null
+++ b/regress/side-status-click.sh
@@ -0,0 +1,77 @@
+#!/bin/sh
+
+# Clicking a window on the side status line, including the current window,
+# dispatches the Status binding with that window.
+
+PATH=/bin:/usr/bin
+TERM=screen
+LC_ALL=C.UTF-8
+export PATH TERM LC_ALL
+
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+TMUX="$TEST_TMUX -LtestA$$ -f/dev/null"
+TMUX2="$TEST_TMUX -LtestB$$ -f/dev/null"
+
+cleanup()
+{
+	$TMUX2 kill-server >/dev/null 2>&1
+	$TMUX kill-server >/dev/null 2>&1
+}
+trap cleanup 0 1 15
+
+fail()
+{
+	echo "$*" >&2
+	exit 1
+}
+
+# Click row $1 of the side status line and check the binding got $2.
+click()
+{
+	$TMUX set -g @click none || exit 1
+	seq=$(printf '\033[<0;3;%sM\033[<0;3;%sm' "$1" "$1")
+	$TMUX2 send-keys -t outer:0.0 -l "$seq" || fail "send mouse failed"
+	sleep 1
+	got=$($TMUX show -gv @click)
+	[ "$got" = "$2" ] || fail "row $1: got '$got', expected '$2'"
+}
+
+$TMUX new-session -d -s inner -n zero -x 60 -y 20 'sleep 100' || exit 1
+$TMUX new-window -d -n one 'sleep 100' || exit 1
+$TMUX new-window -d -n two 'sleep 100' || exit 1
+$TMUX set -g mouse on || exit 1
+$TMUX set -g status off || exit 1
+$TMUX set -g side-status left || exit 1
+$TMUX bind -n MouseDown1Status \
+    set -gF @click '#{mouse_status_range} #{window_name}' || exit 1
+$TMUX bind -n MouseDown1StatusDefault set -g @click default || exit 1
+$TMUX2 new-session -d -s outer -x 60 -y 20 'sleep 100' || exit 1
+$TMUX2 set -g status off || exit 1
+$TMUX2 respawn-pane -k -t outer:0.0 "$TMUX attach -t inner" || exit 1
+sleep 1
+
+# The current window is first, then in the middle of the list.
+click 1 'window zero'
+click 2 'window one'
+click 4 default
+$TMUX select-window -t inner:1 || exit 1
+sleep 0.5
+click 1 'window zero'
+click 2 'window one'
+click 3 'window two'
+
+# A range closed in the same style as the line break ends on its own row.
+$TMUX set -g side-status-format '#[range=user|foo]one#[norange,nl]two' ||
+    exit 1
+sleep 0.5
+click 1 'foo one'
+click 2 default
+
+# A range still open at a line break carries on to the next row.
+$TMUX set -g side-status-format '#[range=user|foo]one#[nl]two#[norange]' ||
+    exit 1
+sleep 0.5
+click 1 'foo one'
+click 2 'foo one'
+
+exit 0
diff --git a/regress/side-status-drag.sh b/regress/side-status-drag.sh
new file mode 100644
index 000000000..ffa515880
--- /dev/null
+++ b/regress/side-status-drag.sh
@@ -0,0 +1,90 @@
+#!/bin/sh
+
+# A Ctrl-drag starting on the side status line must not create a floating
+# pane, and must still dispatch Status bindings. Ctrl-clicking a window on the
+# side status line swaps windows, so panes are compared across the session.
+
+PATH=/bin:/usr/bin
+TERM=screen
+export PATH TERM
+
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+TMUX="$TEST_TMUX -LtestA$$ -f/dev/null"
+TMUX2="$TEST_TMUX -LtestB$$ -f/dev/null"
+
+cleanup()
+{
+	$TMUX2 kill-server >/dev/null 2>&1
+	$TMUX kill-server >/dev/null 2>&1
+}
+trap cleanup 0 1 15
+
+fail()
+{
+	echo "$*" >&2
+	exit 1
+}
+
+mouse()
+{
+	seq=$(printf '\033[<%s;%s;%s%s' "$1" "$2" "$3" "$4")
+	$TMUX2 send-keys -t outer:0.0 -l "$seq" || fail "send mouse failed"
+	sleep 0.2
+}
+
+check_drag()
+{
+	sx=$1
+	sy=$2
+	ex=$3
+	ey=$4
+
+	# First move along the side status line, then into the pane.
+	mouse 16 "$sx" "$sy" M
+	mouse 48 "$sx" $((sy + 1)) M
+	mouse 48 "$ex" "$ey" M
+	mouse 48 $((ex + 2)) "$ey" M
+	mouse 16 $((ex + 2)) "$ey" m
+
+	panes=$($TMUX list-panes -s -F '#{pane_id}') || fail "server exited"
+	panes=$(echo "$panes" | sort)
+	[ "$panes" = "$BASE" ] ||
+	    fail "side status drag from $sx,$sy created a pane: $panes"
+}
+
+$TMUX new-session -d -s inner -x 60 -y 20 'sleep 100' || exit 1
+$TMUX new-window -d 'sleep 100' || exit 1
+$TMUX set -g mouse on || exit 1
+$TMUX set -g default-command 'sleep 100' || exit 1
+$TMUX set -g status off || exit 1
+$TMUX set -g side-status left || exit 1
+BASE=$($TMUX list-panes -s -F '#{pane_id}') || exit 1
+BASE=$(echo "$BASE" | sort)
+$TMUX2 new-session -d -s outer -x 60 -y 20 'sleep 100' || exit 1
+$TMUX2 set -g status off || exit 1
+$TMUX2 respawn-pane -k -t outer:0.0 "$TMUX attach -t inner" || exit 1
+sleep 1
+
+# Blank rows and the window list on the left.
+check_drag 3 10 30 12
+check_drag 2 1 30 12
+check_drag 2 2 30 12
+
+$TMUX set -g side-status right || exit 1
+sleep 0.5
+check_drag 55 10 20 12
+
+# The horizontal status line takes the bottom row below the side status.
+$TMUX set -g side-status left || exit 1
+$TMUX set -g status on || exit 1
+sleep 0.5
+check_drag 3 10 30 12
+
+# A drag starting on a window range dispatches the Status binding.
+$TMUX bind -n C-MouseDrag1Status set -g @status-drag status || exit 1
+$TMUX set -g @status-drag '' || exit 1
+check_drag 2 2 30 12
+got=$($TMUX show -gv @status-drag)
+[ "$got" = status ] || fail "got drag '$got', expected 'status'"
+
+exit 0
diff --git a/regress/side-status-format.sh b/regress/side-status-format.sh
new file mode 100644
index 000000000..5f8501a2d
--- /dev/null
+++ b/regress/side-status-format.sh
@@ -0,0 +1,139 @@
+#!/bin/sh
+
+# Split formats into lines, preserve headers and footers while scrolling,
+# and clip wide or combining characters at the side status boundary.
+
+PATH=/bin:/usr/bin
+TERM=screen
+LC_ALL=C.UTF-8
+export PATH TERM LC_ALL
+
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+TMUX="$TEST_TMUX -LtestA$$ -f/dev/null"
+TMUX2="$TEST_TMUX -LtestB$$ -f/dev/null"
+DIR=$(mktemp -d) || exit 1
+HEIGHT=8
+
+cleanup()
+{
+	$TMUX2 kill-server >/dev/null 2>&1
+	$TMUX kill-server >/dev/null 2>&1
+	rm -f "$DIR/actual" "$DIR/expected"
+	rmdir "$DIR"
+}
+trap cleanup 0 1 15
+
+check()
+{
+	format=$1
+	shift
+	$TMUX set -g side-status-format "$format" || exit 1
+	: >"$DIR/expected"
+	n=0
+	for line in "$@"; do
+		printf '%s\n' "$line" >>"$DIR/expected"
+		n=$((n + 1))
+	done
+	while [ "$n" -lt "$HEIGHT" ]; do
+		printf '       │\n' >>"$DIR/expected"
+		n=$((n + 1))
+	done
+	i=0
+	while [ "$i" -lt 50 ]; do
+		$TMUX2 capture-pane -p -t outer:0.0 >"$DIR/actual" || exit 1
+		cmp -s "$DIR/actual" "$DIR/expected" && return
+		sleep 0.1
+		i=$((i + 1))
+	done
+	echo "format '$format' at height $HEIGHT differs:" >&2
+	diff -u "$DIR/expected" "$DIR/actual" >&2
+	exit 1
+}
+
+resize()
+{
+	HEIGHT=$1
+	$TMUX2 resize-window -t outer:0 -y "$HEIGHT" || exit 1
+}
+
+$TMUX new-session -d -s inner -x 40 -y 8 'sleep 100' || exit 1
+$TMUX set -g status off || exit 1
+$TMUX set -g side-status left || exit 1
+$TMUX set -g side-status-width 8 || exit 1
+$TMUX2 new-session -d -s outer -x 40 -y 8 'sleep 100' || exit 1
+$TMUX2 set -g status off || exit 1
+$TMUX2 set -g window-size manual || exit 1
+$TMUX2 respawn-pane -k -t outer:0.0 "$TMUX attach -t inner" || exit 1
+sleep 1
+
+# Empty, consecutive, leading and trailing breaks, with both spellings.
+check ''
+check 'one#[nl]#[nl]three#[nl]' 'one    │' '       │' 'three  │'
+check '
+
+three
+' '       │' '       │' 'three  │'
+check 'one
+two' 'one    │' 'two    │'
+
+# Escaped hashes must not turn literal text into a line break.
+check '##[nl]#[nl]two' '#[nl]  │' 'two    │'
+check '####[nl]#[nl]two' '##[nl] │' 'two    │'
+check '###[nl]two' '#      │' 'two    │'
+check 'one##' 'one#   │'
+
+# Invalid or unfinished styles do not consume the following valid lines.
+check 'one#[invalid-style]two#[nl]three' 'onetwo │' 'three  │'
+check 'one#[unfinished' 'one    │'
+check '#[ignore]A#[nl]B
+C' 'A#[nl]B│' 'C      │'
+
+# Alignment carries over a break, as do character widths.
+check '#[align=centre]X#[nl]Y' '   X   │' '   Y   │'
+check '#[align=absolute-centre]X#[nl]Y' '   X   │' '   Y   │'
+check 'abcde界#[nl]abcdef界#[nl]abcdeéf' \
+    'abcde界│' 'abcdef │' 'abcdeéf│'
+
+format='H1#[nl]H2#[nl]#[list=on]L0#[nl]L1#[nl]'
+format=$format'#[list=focus]L2#[nl]#[list=on]L3#[nl]L4#[nl]'
+format=$format'#[nolist]F1#[nl]F2'
+check "$format" 'H1     │' 'H2     │' 'L0     │' 'L1     │' \
+    'L2     │' 'L3     │' 'F1     │' 'F2     │'
+resize 6
+check "$format" 'H1     │' 'H2     │' 'L1     │' 'L2     │' \
+    'F1     │' 'F2     │'
+resize 4
+check "$format" 'H1     │' 'H2     │' 'F1     │' 'F2     │'
+resize 3
+check "$format" 'H1     │' 'H2     │' 'F1     │'
+resize 1
+check "$format" 'H1     │'
+
+# Markers consume only list lines and cannot replace the focused line.
+format='H#[nl]#[list=on]#[list=left-marker]^#[nl]'
+format=$format'#[list=right-marker]v#[nl]#[list=on]L0#[nl]L1#[nl]'
+format=$format'#[list=focus]L2#[nl]#[list=on]L3#[nl]L4#[nl]'
+format=$format'#[nolist]F'
+resize 5
+check "$format" 'H      │' '^      │' 'L2     │' 'v      │' 'F      │'
+resize 3
+check "$format" 'H      │' 'L2     │' 'F      │'
+resize 2
+check "$format" 'H      │' 'F      │'
+
+# A large logical list does not require a tall terminal.
+format=$(awk 'BEGIN {
+	printf "H#[nl]#[list=on]"
+	for (i = 0; i < 1000; i++) {
+		if (i == 800)
+			printf "#[list=focus]"
+		if (i == 801)
+			printf "#[list=on]"
+		printf "L%d#[nl]", i
+	}
+	printf "#[nolist]F"
+}')
+resize 3
+check "$format" 'H      │' 'L800   │' 'F      │'
+
+exit 0
diff --git a/regress/side-status-image.sh b/regress/side-status-image.sh
new file mode 100644
index 000000000..2d52f3265
--- /dev/null
+++ b/regress/side-status-image.sh
@@ -0,0 +1,78 @@
+#!/bin/sh
+
+# Images are drawn and erased in the pane's columns with either side status
+# position and with the horizontal status off, above or below the window.
+
+PATH=/bin:/usr/bin
+TERM=screen
+export TERM
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+
+python3 -B - "$TEST_TMUX" <<'PY'
+import sys
+from image_test import image_test, sixel
+from image_terminal import Terminal
+
+side = 14
+w, h = 16, 32
+wire = sixel(w, h, [(100, 0, 0)], [0] * (w * h))
+
+def placed(cx, cy):
+    return {(cx * 8 + x, cy * 16 + y): (255, 0, 0)
+        for y in range(h) for x in range(w)}
+
+def side_cells(terminal, xoff, yoff, height):
+    return {(x, y): terminal.cells.get((x, y))
+        for y in range(yoff, yoff + height)
+        for x in range(xoff, xoff + side)}
+
+def check(position, status):
+    with image_test(sys.argv[1]) as test:
+        test.run("set-option", "-g", "side-status", position)
+        test.run("set-option", "-g", "side-status-width", str(side))
+        if status != "off":
+            test.run("set-option", "-g", "status", "2")
+            test.run("set-option", "-g", "status-position", status)
+        xoff = side if position == "left" else 0
+        yoff = 2 if status == "top" else 0
+        height = 16 if status == "off" else 14
+        side_x = 0 if position == "left" else 40 - side
+        separator = side - 1 if position == "left" else side_x
+        client = test.attach()
+        test.emit(b'\033[3;3H' + wire)
+
+        # A full redraw.
+        test.redraw()
+        terminal = Terminal()
+        terminal.feed(client.data)
+        terminal.check(placed(xoff + 2, yoff + 2))
+        cells = side_cells(terminal, side_x, yoff, height)
+        assert all(cells[separator, y] not in (None, ' ')
+            for y in range(yoff, yoff + height)), \
+            (position, status, 'side status line not drawn')
+
+        # Inserting a line above the image redraws the damaged area.
+        test.emit(b'\033[3;1H\033[L')
+        terminal.feed(client.data)
+        terminal.check(placed(xoff + 2, yoff + 3))
+        assert side_cells(terminal, side_x, yoff, height) == cells, \
+            (position, status, 'side status erased by damage')
+
+        # Leaving copy mode redraws only the pane.
+        client.clear()
+        test.run("copy-mode")
+        test.wait(lambda: test.run("display-message", "-p",
+            "#{pane_in_mode}") == "1")
+        test.run("send-keys", "-X", "cancel")
+        test.wait(lambda: test.run("display-message", "-p",
+            "#{pane_in_mode}") == "0")
+        client.read(0.2)
+        terminal.feed(client.data)
+        terminal.check(placed(xoff + 2, yoff + 3))
+        assert side_cells(terminal, side_x, yoff, height) == cells, \
+            (position, status, 'side status erased by pane redraw')
+
+for position in ("left", "right"):
+    for status in ("off", "top", "bottom"):
+        check(position, status)
+PY
diff --git a/regress/side-status-margins.sh b/regress/side-status-margins.sh
new file mode 100644
index 000000000..4f8f789c9
--- /dev/null
+++ b/regress/side-status-margins.sh
@@ -0,0 +1,72 @@
+#!/bin/sh
+
+# On a terminal with left and right margins, scrolling a pane beside the side
+# status line sets the margins to the pane's columns. The inner client is
+# told the terminal has margins and its output is recorded raw from the outer
+# pane, where ESC [ left ; right s sets the margins (1-based).
+
+PATH=/bin:/usr/bin
+TERM=screen
+LC_ALL=C.UTF-8
+export PATH TERM LC_ALL
+
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+TMUX="$TEST_TMUX -LtestA$$ -f/dev/null"
+TMUX2="$TEST_TMUX -LtestB$$ -f/dev/null"
+
+DIR=$(mktemp -d) || exit 1
+TRIGGER=$DIR/trigger
+OUT=$DIR/out
+
+cleanup()
+{
+	$TMUX2 kill-server >/dev/null 2>&1
+	$TMUX kill-server >/dev/null 2>&1
+	rm -f "$TRIGGER" "$OUT"
+	rmdir "$DIR"
+}
+trap cleanup 0 1 15
+
+fail()
+{
+	echo "$*" >&2
+	exit 1
+}
+
+# Scroll a full width pane with the side status line on side $1 and check the
+# margins sent are $2.
+check()
+{
+	$TMUX kill-server >/dev/null 2>&1
+	$TMUX2 kill-server >/dev/null 2>&1
+	rm -f "$TRIGGER" "$OUT"
+
+	$TMUX new-session -d -s inner -x 60 -y 10 "sh -c '
+		while [ ! -e $TRIGGER ]; do sleep 0.1; done
+		i=0
+		while [ \$i -lt 15 ]; do i=\$((i + 1)); echo line\$i; done
+		exec sleep 100'" || exit 1
+	$TMUX set -g status off || exit 1
+	$TMUX set -g side-status "$1" || exit 1
+	$TMUX set -as terminal-features ',*:margins' || exit 1
+	$TMUX2 new-session -d -s outer -x 60 -y 10 'sleep 100' || exit 1
+	$TMUX2 set -g status off || exit 1
+	$TMUX2 respawn-pane -k -t outer:0.0 "$TMUX attach -t inner" || exit 1
+	sleep 1
+	$TMUX2 pipe-pane -t outer:0.0 "cat >$OUT" || exit 1
+	sleep 0.5
+	: >"$TRIGGER"
+	sleep 1
+
+	got=$(tr '\033' E <"$OUT" | grep -o 'E\[[0-9]*;[0-9]*s' | sort -u |
+	    tr -d 'E[s' | tr '\n' ' ')
+	[ "$got" = "$2 " ] || fail "side-status $1: margins '$got', expected '$2'"
+}
+
+# Pane in columns 15 to 60 after a left side status line of width 14.
+check left '15;60'
+
+# Pane in columns 1 to 46 before a right side status line.
+check right '1;46'
+
+exit 0
diff --git a/regress/side-status-mouse.sh b/regress/side-status-mouse.sh
new file mode 100644
index 000000000..ebeafa3cf
--- /dev/null
+++ b/regress/side-status-mouse.sh
@@ -0,0 +1,109 @@
+#!/bin/sh
+
+# Status coordinates and session/window targets on either side, with the
+# horizontal status off, above or below the window.
+
+PATH=/bin:/usr/bin
+TERM=screen
+LC_ALL=C.UTF-8
+export PATH TERM LC_ALL
+
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+TMUX="$TEST_TMUX -LtestA$$ -f/dev/null"
+TMUX2="$TEST_TMUX -LtestB$$ -f/dev/null"
+
+cleanup()
+{
+	$TMUX2 kill-server >/dev/null 2>&1
+	$TMUX kill-server >/dev/null 2>&1
+}
+trap cleanup 0 1 15
+
+click()
+{
+	expected="$3|$(($1 - 1))|$(($2 - 1))"
+	$TMUX set -g @mouse none || exit 1
+	seq=$(printf '\033[<0;%s;%sM\033[<0;%s;%sm' "$1" "$2" "$1" "$2")
+	$TMUX2 send-keys -t outer:0.0 -l "$seq" || exit 1
+	i=0
+	while [ "$i" -lt 50 ]; do
+		got=$($TMUX show -gv @mouse)
+		[ "$got" = "$expected" ] && break
+		sleep 0.1
+		i=$((i + 1))
+	done
+	[ "$got" = "$expected" ] || {
+		echo "$side/$status at $1,$2: '$got', expected '$expected'" >&2
+		exit 1
+	}
+	sleep 0.5
+}
+
+$TMUX new-session -d -s inner -n zero -x 80 -y 20 'sleep 100' || exit 1
+$TMUX new-window -d -n one 'sleep 100' || exit 1
+$TMUX new-session -d -s beta -n other -x 100 -y 30 'sleep 100' || exit 1
+$TMUX set -g mouse on || exit 1
+$TMUX set -g automatic-rename off || exit 1
+$TMUX set -g side-status-width 14 || exit 1
+[ "$($TMUX display -p '#{mouse_absolute_x}|#{mouse_absolute_y}')" = '|' ] ||
+    exit 1
+$TMUX set -g 'status-format[0]' \
+    '#[range=window|1]window#[norange]' || exit 1
+$TMUX set -g 'status-format[1]' 'second' || exit 1
+format='#{mouse_status_range}|#{mouse_status_line}|#{mouse_x}|#{mouse_y}'
+format=$format'|#{session_name}|#{window_name}'
+format=$format'|#{mouse_absolute_x}|#{mouse_absolute_y}'
+for key in MouseDown1Status MouseDown1StatusDefault MouseDown1StatusBorder \
+    MouseDown1Pane; do
+	$TMUX bind -n "$key" set -gF @mouse "$format" || exit 1
+done
+$TMUX2 new-session -d -s outer -x 80 -y 20 'sleep 100' || exit 1
+$TMUX2 set -g status off || exit 1
+$TMUX2 respawn-pane -k -t outer:0.0 "$TMUX attach -t inner" || exit 1
+sleep 1
+
+for side in left right; do
+	$TMUX set -g side-status "$side" || exit 1
+	if [ "$side" = left ]; then
+		column=3
+		separator=14
+		pane_column=17
+		separator_x=13
+	else
+		column=69
+		separator=67
+		pane_column=3
+		separator_x=0
+	fi
+	for status in off top bottom; do
+		offset=0
+		if [ "$status" = off ]; then
+			$TMUX set -g status off || exit 1
+		else
+			$TMUX set -g status 2 || exit 1
+			$TMUX set -g status-position "$status" || exit 1
+			[ "$status" = top ] && offset=2
+		fi
+		sleep 0.5
+
+		# The current session's windows are between the session headers.
+		click "$column" "$((offset + 1))" 'session|0|2|0|inner|zero'
+		click "$((column + 3))" "$((offset + 3))" \
+		    'window|2|5|2|inner|one'
+		click "$column" "$((offset + 4))" 'session|3|2|3|beta|other'
+		click "$separator" "$((offset + 6))" \
+		    "|5|$separator_x|5|inner|zero"
+		click "$pane_column" "$((offset + 7))" '||2|6|inner|zero'
+
+		# Horizontal status coordinates are relative to its first line,
+		# even if the clicked window's pane extends behind the status.
+		if [ "$status" != off ]; then
+			line=1
+			[ "$status" = bottom ] && line=19
+			click 3 "$line" 'window|0|2|0|inner|one'
+			click 3 "$((line + 1))" '|1|2|1|inner|zero'
+		fi
+	done
+done
+
+exit 0
diff --git a/regress/side-status-off-redraw.sh b/regress/side-status-off-redraw.sh
new file mode 100644
index 000000000..b10a99891
--- /dev/null
+++ b/regress/side-status-off-redraw.sh
@@ -0,0 +1,55 @@
+#!/bin/sh
+
+# With the side status line off, a full redraw after changing window still
+# draws pane border status lines that have not changed.
+
+PATH=/bin:/usr/bin
+TERM=screen
+LC_ALL=C.UTF-8
+export PATH TERM LC_ALL
+
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+TMUX="$TEST_TMUX -LtestA$$ -f/dev/null"
+TMUX2="$TEST_TMUX -LtestB$$ -f/dev/null"
+
+cleanup()
+{
+	$TMUX2 kill-server >/dev/null 2>&1
+	$TMUX kill-server >/dev/null 2>&1
+}
+trap cleanup 0 1 15
+
+fail()
+{
+	echo "$*" >&2
+	exit 1
+}
+
+check()
+{
+	got=$($TMUX2 capture-pane -p -t outer:0.0 | head -n 1)
+	[ "$got" = "$2" ] || fail "$1: top row is '$got', expected '$2'"
+}
+
+$TMUX new-session -d -s inner -x 40 -y 10 'sleep 100' || exit 1
+$TMUX set -g status off || exit 1
+$TMUX set -g pane-border-status top || exit 1
+$TMUX set -g pane-border-format ' #{pane_index} ' || exit 1
+$TMUX split-window -h 'sleep 100' || exit 1
+$TMUX new-window 'sleep 100' || exit 1
+$TMUX select-window -t:0 || exit 1
+$TMUX2 new-session -d -s outer -x 40 -y 10 'sleep 100' || exit 1
+$TMUX2 set -g status off || exit 1
+$TMUX2 respawn-pane -k -t outer:0.0 "$TMUX attach -t inner" || exit 1
+sleep 1
+
+SPLIT='── 0 ───────────────┬── 1 ──────────────'
+check attach "$SPLIT"
+
+$TMUX select-window -t:1 || exit 1
+sleep 0.5
+$TMUX select-window -t:0 || exit 1
+sleep 0.5
+check "after select-window" "$SPLIT"
+
+exit 0
diff --git a/regress/side-status-pane-drag.sh b/regress/side-status-pane-drag.sh
new file mode 100644
index 000000000..9f3e4b5ff
--- /dev/null
+++ b/regress/side-status-pane-drag.sh
@@ -0,0 +1,113 @@
+#!/bin/sh
+
+# Creating, moving and resizing panes must use window coordinates with a
+# side status line, including when the horizontal status is at the top.
+
+PATH=/bin:/usr/bin
+TERM=screen
+export PATH TERM
+
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+TMUX="$TEST_TMUX -LtestA$$ -f/dev/null"
+TMUX2="$TEST_TMUX -LtestB$$ -f/dev/null"
+
+cleanup()
+{
+	$TMUX2 kill-server >/dev/null 2>&1
+	$TMUX kill-server >/dev/null 2>&1
+}
+trap cleanup 0 1 15
+
+fail()
+{
+	echo "$side/$status: $*" >&2
+	exit 1
+}
+
+# Send window coordinates as one-based terminal coordinates.
+mouse()
+{
+	seq=$(printf '\033[<%s;%s;%s%s' "$1" \
+	    "$(( $2 + xoff + 1 ))" "$(( $3 + yoff + 1 ))" "$4")
+	$TMUX2 send-keys -t outer:0.0 -l "$seq" || fail "send mouse failed"
+	sleep 0.2
+}
+
+drag()
+{
+	mouse "$1" "$2" "$3" M
+	mouse "$(( $1 + 32 ))" "$4" "$5" M
+	mouse "$1" "$4" "$5" m
+}
+
+check()
+{
+	i=0
+	while [ "$i" -lt 50 ]; do
+		got=$($TMUX display -p -t "$1" \
+		    '#{pane_left},#{pane_top},#{pane_width},#{pane_height}')
+		[ "$got" = "$2" ] && return
+		sleep 0.1
+		i=$((i + 1))
+	done
+	fail "pane $1: got '$got', expected '$2'"
+}
+
+$TMUX new-session -d -s inner -x 80 -y 24 'sleep 100' || exit 1
+$TMUX set -g mouse on || exit 1
+$TMUX set -g default-command 'sleep 100' || exit 1
+$TMUX set -g side-status-width 14 || exit 1
+BASE=$($TMUX display -p '#{pane_id}') || exit 1
+$TMUX2 new-session -d -s outer -x 80 -y 24 'sleep 100' || exit 1
+$TMUX2 set -g status off || exit 1
+$TMUX2 respawn-pane -k -t outer:0.0 "$TMUX attach -t inner" || exit 1
+sleep 1
+
+for side in left right; do
+	$TMUX set -g side-status "$side" || exit 1
+	xoff=0
+	[ "$side" = left ] && xoff=14
+	for status in off top bottom; do
+		yoff=0
+		if [ "$status" = off ]; then
+			$TMUX set -g status off || exit 1
+		else
+			$TMUX set -g status 2 || exit 1
+			$TMUX set -g status-position "$status" || exit 1
+			[ "$status" = top ] && yoff=2
+		fi
+		sleep 0.5
+
+		# Ctrl-drag creates a floating pane inside the rectangle.
+		drag 16 2 1 10 5
+		id=$($TMUX list-panes -F \
+		    '#{?pane_floating_flag,#{pane_id},}' | tail -1)
+		[ -n "$id" ] || fail "drag did not create a floating pane"
+		check "$id" '3,2,7,3'
+		$TMUX kill-pane -t "$id" || exit 1
+
+		# Alt-drag moves a floating pane without changing its size.
+		id=$($TMUX new-pane -dPF '#{pane_id}' \
+		    -x 14 -y 7 -X 5 -Y 3 'sleep 100') || exit 1
+		check "$id" '6,4,12,5'
+		drag 8 8 5 12 7
+		check "$id" '10,6,12,5'
+
+		# Dragging the bottom right border resizes both dimensions.
+		drag 0 22 11 25 13
+		check "$id" '10,6,15,7'
+		$TMUX kill-pane -t "$id" || exit 1
+
+		# The same terminal offsets apply to tiled pane borders.
+		id=$($TMUX split-window -dhPF '#{pane_id}' \
+		    -t "$BASE" 'sleep 100') || exit 1
+		width=$($TMUX display -p -t "$BASE" '#{pane_width}')
+		drag 0 "$width" 5 "$((width + 4))" 5
+		got=$($TMUX display -p -t "$BASE" '#{pane_width}')
+		[ "$got" = "$((width + 4))" ] ||
+		    fail "tiled width: got '$got', expected '$((width + 4))'"
+		$TMUX kill-pane -t "$id" || exit 1
+	done
+done
+
+exit 0
diff --git a/regress/side-status-prompt.sh b/regress/side-status-prompt.sh
new file mode 100644
index 000000000..db0e3ad67
--- /dev/null
+++ b/regress/side-status-prompt.sh
@@ -0,0 +1,83 @@
+#!/bin/sh
+
+# A pane prompt redrawn after the pane scrolls stays beside the side status
+# line. With side-status left the pane is not full width, so scrolling is
+# redrawn as damage, which draws the prompt again over the pane.
+
+PATH=/bin:/usr/bin
+TERM=screen
+LC_ALL=C.UTF-8
+export PATH TERM LC_ALL
+
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+TMUX="$TEST_TMUX -LtestA$$ -f/dev/null"
+TMUX2="$TEST_TMUX -LtestB$$ -f/dev/null"
+
+DIR=$(mktemp -d) || exit 1
+TRIGGER=$DIR/trigger
+CAPTURE=$DIR/capture
+
+cleanup()
+{
+	$TMUX2 kill-server >/dev/null 2>&1
+	$TMUX kill-server >/dev/null 2>&1
+	rm -rf "$DIR"
+}
+trap cleanup 0 1 15
+
+fail()
+{
+	echo "$*" >&2
+	[ -s "$CAPTURE" ] && cat "$CAPTURE" >&2
+	exit 1
+}
+
+wait_outer_has()
+{
+	i=0
+	while [ "$i" -lt 50 ]; do
+		$TMUX2 capture-pane -p -t outer:0.0 >"$CAPTURE" 2>/dev/null
+		grep -q "$1" "$CAPTURE" && return 0
+		sleep 0.1
+		i=$((i + 1))
+	done
+	fail "outer client did not show $1"
+}
+
+# The pane waits for the trigger, then prints enough lines to scroll.
+$TMUX new-session -d -s inner -n work -x 60 -y 20 "sh -c '
+	while [ ! -e $TRIGGER ]; do sleep 0.1; done
+	i=0
+	while [ \$i -lt 40 ]; do i=\$((i + 1)); echo line\$i; done
+	exec sleep 100'" || exit 1
+$TMUX set -g status off || exit 1
+$TMUX set -g automatic-rename off || exit 1
+$TMUX set -g side-status left || exit 1
+$TMUX2 new-session -d -s outer -x 60 -y 20 'sleep 100' || exit 1
+$TMUX2 set -g status off || exit 1
+$TMUX2 respawn-pane -k -t outer:0.0 "$TMUX attach -t inner" || exit 1
+
+i=0
+while [ "$i" -lt 50 ]; do
+	CLIENT=$($TMUX list-clients -F '#{client_name}' 2>/dev/null)
+	[ -n "$CLIENT" ] && break
+	sleep 0.1
+	i=$((i + 1))
+done
+[ -n "$CLIENT" ] || fail "inner client did not attach"
+
+$TMUX command-prompt -b -P -t "$CLIENT" -p PROMPTX 'display -p %%' ||
+    exit 1
+wait_outer_has PROMPTX
+
+: >"$TRIGGER"
+wait_outer_has line40
+sleep 0.5
+
+# The bottom row is the side status line followed by the prompt.
+$TMUX2 capture-pane -p -t outer:0.0 >"$CAPTURE" || exit 1
+want="$(printf '%13s' '')│PROMPTX"
+got=$(tail -n 1 "$CAPTURE")
+[ "$got" = "$want" ] || fail "bottom row is '$got', expected '$want'"
+
+exit 0
diff --git a/regress/side-status-refresh.sh b/regress/side-status-refresh.sh
new file mode 100644
index 000000000..9cde7a34c
--- /dev/null
+++ b/regress/side-status-refresh.sh
@@ -0,0 +1,78 @@
+#!/bin/sh
+
+# The side status line must refresh every status-interval seconds on its own,
+# whether or not the horizontal status line is on, and whether it was on when
+# the client attached or turned on afterwards. The client status timer drives
+# both lines, so this checks it is armed in both cases with status off.
+#
+# The side status line is rendered by an inner tmux attached inside an outer
+# tmux pane. Its format is a #() command which appends a byte to a file each
+# time it runs, and a #() command is run again only when the format is
+# expanded in a later second, so the file grows once per refresh. Nothing in
+# the test asks for a redraw between the two counts, so growth means the
+# timer refreshed the side status line by itself.
+
+PATH=/bin:/usr/bin
+TERM=screen
+LC_ALL=C.UTF-8
+export TERM LC_ALL
+
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+TMUX="$TEST_TMUX -LtestA$$ -f/dev/null"
+TMUX2="$TEST_TMUX -LtestB$$ -f/dev/null"
+
+COUNT1=$(mktemp)
+COUNT2=$(mktemp)
+trap "rm -f $COUNT1 $COUNT2; $TMUX kill-server 2>/dev/null; \
+	$TMUX2 kill-server 2>/dev/null" 0 1 15
+
+fail() {
+	echo "$*" >&2
+	exit 1
+}
+
+count() {
+	wc -c <"$1" | tr -d ' '
+}
+
+# Attach the inner server in an outer pane, then wait for the first draw.
+attach() {
+	$TMUX new -d -x30 -y8 "$TMUX2 attach" || exit 1
+	sleep 1
+}
+
+# Check the side status line refreshed at least twice in three seconds.
+refreshes() {
+	before=$(count "$1")
+	sleep 3
+	after=$(count "$1")
+	[ $((after - before)) -ge 2 ] ||
+	    fail "$2: side status ran $before then $after times, did not refresh"
+}
+
+$TMUX kill-server 2>/dev/null
+$TMUX2 kill-server 2>/dev/null
+
+# Side status on before the client attaches, with status off.
+$TMUX2 new -d -x30 -y8 "sh -c 'exec sleep 100'" || exit 1
+$TMUX2 set -g status off || exit 1
+$TMUX2 set -g status-interval 1 || exit 1
+$TMUX2 set -g side-status left || exit 1
+$TMUX2 set -g side-status-format "#(printf x >>$COUNT1)" || exit 1
+attach
+refreshes "$COUNT1" "on at attach"
+
+# Side status turned on after the client attached, with status off. A new
+# inner server so the client timer starts from nothing.
+$TMUX2 kill-server || exit 1
+sleep 1
+$TMUX2 new -d -x30 -y8 "sh -c 'exec sleep 100'" || exit 1
+$TMUX2 set -g status off || exit 1
+$TMUX2 set -g status-interval 1 || exit 1
+$TMUX2 set -g side-status-format "#(printf x >>$COUNT2)" || exit 1
+attach
+$TMUX2 set -g side-status left || exit 1
+sleep 1
+refreshes "$COUNT2" "on after attach"
+
+exit 0
diff --git a/regress/side-status-resize.sh b/regress/side-status-resize.sh
new file mode 100644
index 000000000..3191cc916
--- /dev/null
+++ b/regress/side-status-resize.sh
@@ -0,0 +1,197 @@
+#!/bin/sh
+
+# Drag the separator on either side, including across the moving boundary and
+# horizontal status. Check limits, release, text bindings and a second client.
+
+PATH=/bin:/usr/bin
+TERM=screen
+LC_ALL=C.UTF-8
+export PATH TERM LC_ALL
+
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+TMUX="$TEST_TMUX -LtestA$$ -f/dev/null"
+TMUX2="$TEST_TMUX -LtestB$$ -f/dev/null"
+
+cleanup()
+{
+	$TMUX2 kill-server >/dev/null 2>&1
+	$TMUX kill-server >/dev/null 2>&1
+}
+trap cleanup 0 1 15
+
+fail()
+{
+	echo "$side/$status: $*" >&2
+	exit 1
+}
+
+mouse()
+{
+	seq=$(printf '\033[<%s;%s;%s%s' "$1" "$2" "$3" "$4")
+	$TMUX2 send-keys -t outer:0.0 -l "$seq" || fail "send mouse failed"
+	sleep 0.1
+}
+
+check()
+{
+	i=0
+	while [ "$i" -lt 50 ]; do
+		width=$($TMUX show -Av -t inner side-status-width)
+		window=$($TMUX display -p -t inner '#{window_width}')
+		if [ "$width" = "$1" ] && [ "$window" = "$((80 - $1))" ]; then
+			break
+		fi
+		sleep 0.1
+		i=$((i + 1))
+	done
+	[ "$width,$window" = "$1,$((80 - $1))" ] ||
+	    fail "side/window widths $width/$window, expected $1/$((80 - $1))"
+	column=$1
+	[ "$side" = right ] && column=$((81 - $1))
+	padding=$(printf '%*s' "$((column - 1))" '')
+	for target in outer other; do
+		i=0
+		while [ "$i" -lt 50 ]; do
+			row=$($TMUX2 capture-pane -p -t "$target:0.0" |
+			    sed -n "$((offset + 2))p")
+			case "$row" in
+			"$padding│"*) break ;;
+			esac
+			sleep 0.1
+			i=$((i + 1))
+		done
+		[ "$i" -lt 50 ] || fail "$target: wrong separator column: $row"
+	done
+}
+
+$TMUX new-session -d -s inner -n zero -x 80 -y 20 'sleep 180' || exit 1
+$TMUX set -g mouse on || exit 1
+$TMUX set -g status off || exit 1
+$TMUX set -g side-status-format \
+    '#[range=window|0]window#[norange]' || exit 1
+$TMUX bind -n MouseDrag1Status set -g @text-drag yes || exit 1
+$TMUX bind -n MouseDrag1StatusDefault set -g @blank-drag yes || exit 1
+$TMUX2 new-session -d -s outer -x 80 -y 20 'sleep 180' || exit 1
+$TMUX2 set -g status off || exit 1
+$TMUX2 new-session -d -s other -x 80 -y 20 'sleep 180' || exit 1
+for target in outer other; do
+	$TMUX2 respawn-pane -k -t "$target:0.0" \
+	    "$TMUX attach -t inner" || exit 1
+done
+sleep 1
+
+for side in left right; do
+	$TMUX set -t inner side-status "$side" || exit 1
+	for status in off top bottom; do
+		offset=0
+		if [ "$status" = off ]; then
+			$TMUX set -t inner status off || exit 1
+		else
+			$TMUX set -t inner status 2 || exit 1
+			$TMUX set -t inner status-position "$status" || exit 1
+			[ "$status" = top ] && offset=2
+		fi
+		$TMUX set -t inner side-status-width 14 || exit 1
+		check 14
+		if [ "$side" = left ]; then
+			start=14 grow=20 shrink=10 smallest=1 largest=80
+		else
+			start=67 grow=61 shrink=71 smallest=80 largest=1
+		fi
+
+		# Grow into the window, then shrink past the starting point.
+		mouse 0 "$start" "$((offset + 6))" M
+		mouse 32 "$grow" "$((offset + 6))" M
+		check 20
+		mouse 32 "$shrink" 1 M
+		check 10
+		mouse 32 "$largest" "$((offset + 6))" M
+		check 79
+		mouse 32 "$smallest" "$((offset + 6))" M
+		check 2
+		mouse 0 "$smallest" "$((offset + 6))" m
+
+		# Motion after release must not resize, and the separator stays
+		# draggable at the minimum width.
+		mouse 35 "$grow" "$((offset + 6))" M
+		check 2
+		sleep 0.5
+		start=2
+		[ "$side" = right ] && start=79
+		mouse 0 "$start" "$((offset + 6))" M
+		mouse 32 "$grow" "$((offset + 6))" M
+		check 20
+		mouse 0 "$grow" "$((offset + 6))" m
+		sleep 0.5
+
+		# Dragging text or blank content dispatches its usual binding.
+		text=2
+		[ "$side" = right ] && text=63
+		$TMUX set -g @text-drag no || exit 1
+		mouse 0 "$text" "$((offset + 1))" M
+		mouse 32 "$((text + 1))" "$((offset + 1))" M
+		mouse 32 40 "$((offset + 6))" M
+		mouse 0 40 "$((offset + 6))" m
+		got=$($TMUX show -gv @text-drag)
+		[ "$got" = yes ] || fail "text drag binding did not fire"
+		check 20
+		sleep 0.5
+		$TMUX set -g @blank-drag no || exit 1
+		mouse 0 "$text" "$((offset + 8))" M
+		mouse 32 40 "$((offset + 8))" M
+		mouse 0 40 "$((offset + 8))" m
+		got=$($TMUX show -gv @blank-drag)
+		[ "$got" = yes ] || fail "blank drag binding did not fire"
+		check 20
+
+		# A modified drag on the separator does not resize it.
+		mouse 16 "$grow" "$((offset + 6))" M
+		mouse 48 40 "$((offset + 6))" M
+		mouse 16 40 "$((offset + 6))" m
+		check 20
+		if [ "$status" != off ]; then
+			line=1
+			[ "$status" = bottom ] && line=19
+			mouse 0 "$grow" "$line" M
+			mouse 32 40 "$((offset + 6))" M
+			mouse 0 40 "$((offset + 6))" m
+			check 20
+		fi
+		[ "$($TMUX show -gv side-status-width)" = 14 ] ||
+		    fail "drag changed the global width"
+
+		# Double-click removes the local width and inherits the default.
+		sleep 0.5
+		seq=$(printf '\033[<0;%s;%sM\033[<0;%s;%sm' \
+		    "$grow" "$((offset + 6))" "$grow" "$((offset + 6))")
+		$TMUX2 send-keys -t outer:0.0 -l "$seq$seq" || exit 1
+		check 14
+		[ -z "$($TMUX show -v -q -t inner side-status-width)" ] ||
+		    fail "double-click did not remove the local width"
+	done
+done
+
+# The resize action is an ordinary binding and can be replaced or removed.
+$TMUX set -t inner side-status-width 20 || exit 1
+check 20
+$TMUX set -g @border-drag no || exit 1
+$TMUX set -g @border-end no || exit 1
+$TMUX bind -n MouseDrag1StatusBorder \
+    set -gF @border-drag '#{mouse_absolute_x},#{mouse_absolute_y}' || exit 1
+$TMUX bind -n MouseDragEnd1StatusBorder set -g @border-end yes || exit 1
+mouse 0 61 6 M
+mouse 32 40 6 M
+mouse 32 42 6 M
+mouse 0 42 6 m
+check 20
+[ "$($TMUX show -gv @border-drag)" = 41,5 ] ||
+    fail "custom border binding did not get the terminal coordinates"
+[ "$($TMUX show -gv @border-end)" = yes ] ||
+    fail "border drag end binding did not fire"
+$TMUX unbind -n MouseDrag1StatusBorder || exit 1
+mouse 0 61 6 M
+mouse 32 40 6 M
+mouse 0 40 6 m
+check 20
+
+exit 0
diff --git a/regress/side-status-results/side-left-floating.result b/regress/side-status-results/side-left-floating.result
new file mode 100644
index 000000000..36e51977a
--- /dev/null
+++ b/regress/side-status-results/side-left-floating.result
@@ -0,0 +1,24 @@
+0:editor     │┌──────────┐
+1:server*    ││FLOAT     │
+2:logs-      ││          │
+             │└──────────┘
+             │
+             │
+             │
+             │
+             │
+             │
+             │
+             │
+             │
+             │
+             │
+             │
+             │
+             │
+             │
+             │
+             │
+             │
+             │
+             │
diff --git a/regress/side-status-results/side-left.result b/regress/side-status-results/side-left.result
new file mode 100644
index 000000000..f0f886a52
--- /dev/null
+++ b/regress/side-status-results/side-left.result
@@ -0,0 +1,24 @@
+0:editor     │SERVER
+1:server*    │
+2:logs-      │
+             │
+             │
+             │
+             │
+             │
+             │
+             │
+             │
+             │
+             │
+             │
+             │
+             │
+             │
+             │
+             │
+             │
+             │
+             │
+             │
+             │
diff --git a/regress/side-status-results/side-off.result b/regress/side-status-results/side-off.result
new file mode 100644
index 000000000..8a939862a
--- /dev/null
+++ b/regress/side-status-results/side-off.result
@@ -0,0 +1,24 @@
+SERVER
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+[test]0:editor  1:server* 2:logs-
diff --git a/regress/side-status-results/side-right-narrow.result b/regress/side-status-results/side-right-narrow.result
new file mode 100644
index 000000000..7e4821bab
--- /dev/null
+++ b/regress/side-status-results/side-right-narrow.result
@@ -0,0 +1,24 @@
+SERVER                                                              │0:editor
+                                                                    │1:server*
+                                                                    │2:logs-
+                                                                    │
+                                                                    │
+                                                                    │
+                                                                    │
+                                                                    │
+                                                                    │
+                                                                    │
+                                                                    │
+                                                                    │
+                                                                    │
+                                                                    │
+                                                                    │
+                                                                    │
+                                                                    │
+                                                                    │
+                                                                    │
+                                                                    │
+                                                                    │
+                                                                    │
+                                                                    │
+[test]0:editor  1:server* 2:logs-
diff --git a/regress/side-status-results/side-right-status.result b/regress/side-status-results/side-right-status.result
new file mode 100644
index 000000000..8fa0afc2e
--- /dev/null
+++ b/regress/side-status-results/side-right-status.result
@@ -0,0 +1,24 @@
+SERVER                                                            │0:editor
+                                                                  │1:server*
+                                                                  │2:logs-
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+[test]0:editor  1:server* 2:logs-
diff --git a/regress/side-status-results/side-right.result b/regress/side-status-results/side-right.result
new file mode 100644
index 000000000..0e5e2a5b6
--- /dev/null
+++ b/regress/side-status-results/side-right.result
@@ -0,0 +1,24 @@
+SERVER                                                            │0:editor
+                                                                  │1:server*
+                                                                  │2:logs-
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
+                                                                  │
diff --git a/regress/side-status-results/side-sessions.result b/regress/side-status-results/side-sessions.result
new file mode 100644
index 000000000..e6e11ef37
--- /dev/null
+++ b/regress/side-status-results/side-sessions.result
@@ -0,0 +1,24 @@
+work                   │SERVER
+├─→ 0:editor           │
+├─→ 1:server*          │
+└─→ 2:logs-            │
+beta                   │
+                       │
+                       │
+                       │
+                       │
+                       │
+                       │
+                       │
+                       │
+                       │
+                       │
+                       │
+                       │
+                       │
+                       │
+                       │
+                       │
+                       │
+                       │
+                       │
diff --git a/regress/side-status-scroll.sh b/regress/side-status-scroll.sh
new file mode 100644
index 000000000..e7972b01a
--- /dev/null
+++ b/regress/side-status-scroll.sh
@@ -0,0 +1,148 @@
+#!/bin/sh
+
+# With more windows than rows, the default side status format scrolls the
+# window list to keep the current window visible and replaces the first and
+# last visible rows with up and down markers.
+
+PATH=/bin:/usr/bin
+TERM=screen
+LC_ALL=C.UTF-8
+export PATH TERM LC_ALL
+
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+TMUX="$TEST_TMUX -LtestA$$ -f/dev/null"
+TMUX2="$TEST_TMUX -LtestB$$ -f/dev/null"
+
+TMP=$(mktemp) || exit 1
+cleanup()
+{
+	$TMUX2 kill-server >/dev/null 2>&1
+	$TMUX kill-server >/dev/null 2>&1
+	rm -f "$TMP"
+}
+trap cleanup 0 1 15
+
+$TMUX new-session -d -s inner -n w0 -x 60 -y 10 'sleep 100' || exit 1
+i=1
+while [ "$i" -lt 15 ]; do
+	$TMUX new-window -d -n "w$i" 'sleep 100' || exit 1
+	i=$((i + 1))
+done
+$TMUX set -g status off || exit 1
+$TMUX set -g side-status left || exit 1
+$TMUX select-window -t inner:7 || exit 1
+$TMUX2 new-session -d -s outer -x 60 -y 10 'sleep 100' || exit 1
+$TMUX2 set -g status off || exit 1
+$TMUX2 respawn-pane -k -t outer:0.0 "$TMUX attach -t inner" || exit 1
+sleep 1
+
+# Compare the outer pane with the expected rows on standard input.
+compare()
+{
+	$TMUX2 capture-pane -p -t outer:0.0 >"$TMP" || exit 1
+	if ! cmp -s - "$TMP"; then
+		echo "$1 differs:" >&2
+		cat "$TMP" >&2
+		exit 1
+	fi
+}
+
+compare "scrolled side status" <<EOF
+↑            │
+3:w3         │
+4:w4         │
+5:w5         │
+6:w6         │
+7:w7*        │
+8:w8         │
+9:w9         │
+10:w10       │
+↓            │
+EOF
+
+# A long current window name in the first row is cut on the right like the
+# other rows.
+$TMUX rename-window -t inner:0 dotfiles-repo || exit 1
+$TMUX select-window -t inner:0 || exit 1
+sleep 1
+compare "first row" <<EOF
+0:dotfiles-re│
+1:w1         │
+2:w2         │
+3:w3         │
+4:w4         │
+5:w5         │
+6:w6         │
+7:w7-        │
+8:w8         │
+↓            │
+EOF
+
+# A format with its list styles in the same order as on the status line, with
+# list=on before the markers, draws the same rows.
+$TMUX set -g side-status-format '#[list=on]#[list=left-marker]^#[nl]'\
+'#[list=right-marker]v#[nl]'\
+'#{W:#[range=window|#{window_index}]#I:#W#[norange]#[nl],'\
+'#[range=window|#{window_index} list=focus]#I:#W*#[norange list=on]#[nl]}' ||
+    exit 1
+$TMUX rename-window -t inner:0 w0 || exit 1
+$TMUX select-window -t inner:7 || exit 1
+sleep 1
+compare "status line order" <<EOF
+^            │
+3:w3         │
+4:w4         │
+5:w5         │
+6:w6         │
+7:w7*        │
+8:w8         │
+9:w9         │
+10:w10       │
+v            │
+EOF
+
+# With list=on at the start of each window row and the focus closed in the
+# current row, a long current window name is still cut on the right.
+$TMUX set -g side-status-format \
+    '#{W:#[list=on]#I:#W#[nl],#[list=on]#[list=focus]#I:#W*#[list=on]#[nl]}' ||
+    exit 1
+$TMUX rename-window -t inner:0 dotfiles-repo || exit 1
+$TMUX select-window -t inner:0 || exit 1
+sleep 1
+compare "list=on rows" <<EOF
+0:dotfiles-re│
+1:w1         │
+2:w2         │
+3:w3         │
+4:w4         │
+5:w5         │
+6:w6         │
+7:w7         │
+8:w8         │
+9:w9         │
+EOF
+
+# With only one or two rows, a marker is not drawn over the current window.
+$TMUX set -gu side-status-format || exit 1
+$TMUX rename-window -t inner:0 w0 || exit 1
+$TMUX select-window -t inner:7 || exit 1
+$TMUX2 resize-window -t outer -y 2 || exit 1
+sleep 1
+compare "two rows" <<EOF
+↑            │
+7:w7*        │
+EOF
+$TMUX select-window -t inner:1 || exit 1
+sleep 1
+compare "two rows at the top" <<EOF
+0:w0         │
+1:w1*        │
+EOF
+$TMUX select-window -t inner:7 || exit 1
+$TMUX2 resize-window -t outer -y 1 || exit 1
+sleep 1
+compare "one row" <<EOF
+7:w7*        │
+EOF
+
+exit 0
diff --git a/regress/side-status-style.sh b/regress/side-status-style.sh
new file mode 100644
index 000000000..1b311f701
--- /dev/null
+++ b/regress/side-status-style.sh
@@ -0,0 +1,81 @@
+#!/bin/sh
+
+# The style at the end of a side status row carries over to the next row, as
+# if the rows were one line: attributes removed from side-status-style stay
+# removed, a pushed or set default stays in place, and the alignment, fill and
+# hyperlink carry on. The inner client runs in an outer pane which is captured
+# with its attributes.
+
+PATH=/bin:/usr/bin
+TERM=screen
+LC_ALL=C.UTF-8
+export PATH TERM LC_ALL
+
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+TMUX="$TEST_TMUX -LtestA$$ -f/dev/null"
+TMUX2="$TEST_TMUX -LtestB$$ -f/dev/null"
+
+cleanup()
+{
+	$TMUX2 kill-server >/dev/null 2>&1
+	$TMUX kill-server >/dev/null 2>&1
+}
+trap cleanup 0 1 15
+
+fail()
+{
+	echo "$*" >&2
+	exit 1
+}
+
+# Check the second side status row starts with $2.
+row2()
+{
+	got=$($TMUX2 capture-pane -ep -t outer:0.0 | sed -n 2p)
+	case "$got" in
+	"$2"*) ;;
+	*) fail "$1: row 2 is '$got'" ;;
+	esac
+}
+
+$TMUX new-session -d -s inner -x 40 -y 10 'sleep 100' || exit 1
+$TMUX set -g status off || exit 1
+$TMUX set -g side-status left || exit 1
+$TMUX2 new-session -d -s outer -x 40 -y 10 'sleep 100' || exit 1
+$TMUX2 set -g status off || exit 1
+$TMUX2 respawn-pane -k -t outer:0.0 "$TMUX attach -t inner" || exit 1
+sleep 1
+
+ESC=$(printf '\033')
+
+$TMUX set -g side-status-style bold || exit 1
+$TMUX set -g side-status-format '#[nobold]one#[nl]two' || exit 1
+sleep 1
+row2 "nobold" "two"
+
+$TMUX set -g side-status-style default || exit 1
+$TMUX set -g side-status-format \
+    '#[fg=red]#[push-default]one#[nl]#[fg=blue]#[default]two' || exit 1
+sleep 1
+row2 "push-default" "$ESC[31mtwo"
+
+$TMUX set -g side-status-format \
+    '#[fg=red]#[set-default]#[fg=blue]#[push-default]one#[nl]'\
+'#[pop-default]#[default]two' || exit 1
+sleep 1
+row2 "set-default" "$ESC[31mtwo"
+
+$TMUX set -g side-status-format '#[align=right]one#[nl]two' || exit 1
+sleep 1
+row2 "align" "          two"
+
+$TMUX set -g side-status-format '#[fill=red]one#[nl]two' || exit 1
+sleep 1
+row2 "fill" "two$ESC[41m"
+
+$TMUX set -g side-status-format '#[link=https://example.com/]one#[nl]two' ||
+    exit 1
+sleep 1
+row2 "link" "$ESC]8;"
+
+exit 0
diff --git a/regress/side-status.sh b/regress/side-status.sh
new file mode 100644
index 000000000..86b58acfd
--- /dev/null
+++ b/regress/side-status.sh
@@ -0,0 +1,89 @@
+#!/bin/sh
+
+# Side status line rendering: geometry on the left and right, a floating pane
+# against the window edge, coexistence with the horizontal status line, width
+# changes and turning it off. Scenes are rendered in an inner tmux attached
+# inside an outer tmux pane; the outer pane is captured and compared with
+# goldens in side-status-results/.
+#
+# Run with GENERATE=1 to (re)create the golden files.
+
+PATH=/bin:/usr/bin
+TERM=screen
+LC_ALL=C.UTF-8
+export TERM LC_ALL
+
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+TMUX="$TEST_TMUX -LtestA$$ -f/dev/null"
+TMUX2="$TEST_TMUX -LtestB$$ -f/dev/null"
+RESULTS=side-status-results
+
+TMP=$(mktemp)
+trap "rm -f $TMP; $TMUX kill-server 2>/dev/null; $TMUX2 kill-server 2>/dev/null" \
+	0 1 15
+
+fail() {
+	echo "$*" >&2
+	exit 1
+}
+
+compare() {
+	sleep 1
+	$TMUX capturep -p >$TMP || exit 1
+	if [ -n "$GENERATE" ]; then
+		cp $TMP "$RESULTS/$1.result" || exit 1
+	else
+		cmp -s $TMP "$RESULTS/$1.result" ||
+		    fail "scene $1 differs from $RESULTS/$1.result"
+	fi
+}
+
+mkdir -p "$RESULTS"
+
+$TMUX kill-server 2>/dev/null
+$TMUX2 kill-server 2>/dev/null
+$TMUX new-session -d -x 80 -y 24 || exit 1
+
+# Inner server with fixed pane content so captures are stable.
+$TMUX2 new-session -d -s work -n editor "sh -c 'printf EDITOR; exec sleep 100'"
+$TMUX2 new-window -n server "sh -c 'printf SERVER; exec sleep 100'"
+$TMUX2 new-window -n logs "sh -c 'printf LOGS; exec sleep 100'"
+$TMUX2 select-window -t:1
+$TMUX2 set -g status off
+$TMUX2 set -g status-left "[test]"
+$TMUX2 set -g status-right ""
+$TMUX2 set -g side-status left
+
+$TMUX send-keys "exec $TEST_TMUX -LtestB$$ -f/dev/null attach" Enter
+sleep 1
+compare side-left
+
+# A floating pane at the window's top left corner sits beside the side status
+# line, not over it.
+id=$($TMUX2 new-pane -dPF '#{pane_id}' -x 12 -y 4 -X 0 -Y 0 \
+    "sh -c 'printf FLOAT; exec sleep 100'") || exit 1
+compare side-left-floating
+$TMUX2 kill-pane -t "$id" || exit 1
+
+$TMUX2 set -g side-status right
+compare side-right
+
+$TMUX2 set -g status on
+compare side-right-status
+
+$TMUX2 set -g side-status-width 12
+compare side-right-narrow
+
+$TMUX2 set -g side-status off
+compare side-off
+
+# A second session collapses the bar into session rows with the current
+# session's windows indented below its row.
+$TMUX2 set -g side-status left
+$TMUX2 set -g side-status-width 24
+$TMUX2 set -g status off
+$TMUX2 new-session -d -s beta -n shell "sh -c 'printf SHELL; exec sleep 100'"
+$TMUX2 refresh-client -S
+compare side-sessions
+
+exit 0
diff --git a/regress/status-ignore-size.sh b/regress/status-ignore-size.sh
index 92950cce9..878b27ed0 100644
--- a/regress/status-ignore-size.sh
+++ b/regress/status-ignore-size.sh
@@ -1,7 +1,7 @@
 #!/bin/sh
 
-# A client attached with ignore-size that is shorter than the status line
-# must have it turned off rather than kill the server.
+# A client attached with ignore-size that is too small for the status line or
+# the side status line must have them turned off rather than kill the server.
 # Each inner client runs in an outer pane of its size.
 
 PATH=/bin:/usr/bin
@@ -51,4 +51,10 @@ $TMUX set -g status 5 || exit 1
 attach 80x24 80x4
 $TMUX has-session 2>/dev/null || fail "server exited: status line too tall"
 
+# A side status line wider than the client.
+$TMUX set -g status on || exit 1
+$TMUX set -g side-status left || exit 1
+attach 80x24 13x24
+$TMUX has-session 2>/dev/null || fail "server exited: side status too wide"
+
 exit 0
diff --git a/regress/status-menu.sh b/regress/status-menu.sh
index 8ef806d69..c49681269 100644
--- a/regress/status-menu.sh
+++ b/regress/status-menu.sh
@@ -1,7 +1,7 @@
 #!/bin/sh
 
-# Status menus are displayed in the visible window and their commands
-# target the clicked window, including when it is not current.
+# Status menus are displayed in the visible window, target the clicked
+# window, and are placed beside the clicked row on either side status line.
 
 PATH=/bin:/usr/bin
 TERM=screen
@@ -29,6 +29,7 @@ fail()
 }
 
 # Right-button press at column $1, row $2 (1-based), targeting window $3.
+# If supplied, $4 is the expected row and column of the first menu item's text.
 check_menu()
 {
 	seq=$(printf '\033[<2;%s;%sM' "$1" "$2")
@@ -42,6 +43,14 @@ check_menu()
 	done
 	grep -q 'Swap Left' "$CAPTURE" || fail "window $3 menu not visible"
 	grep -q "─$3:" "$CAPTURE" || fail "window $3 title missing"
+	if [ -n "$4" ]; then
+		got=$(awk '{
+			gsub(/│/, "|")
+			if (index($0, "Swap Left"))
+				print NR, index($0, "Swap Left")
+		}' "$CAPTURE")
+		[ "$got" = "$4" ] || fail "menu at '$got', expected '$4'"
+	fi
 
 	# Mark acts on the clicked window without selecting it. Other windows
 	# exercise dragging into the menu and releasing the right button.
@@ -81,15 +90,49 @@ $TMUX new-window -d -n one 'sleep 100' || exit 1
 $TMUX new-window -d -n two 'sleep 100' || exit 1
 $TMUX set -g mouse on || exit 1
 $TMUX set -g automatic-rename off || exit 1
-$TMUX set -g status 2 || exit 1
-$TMUX set -g 'status-format[0]' \
-    '#[range=window|0]0:zero#[norange] #[range=window|1]1:one#[norange]' || \
-    exit 1
+$TMUX set -g side-status-width 14 || exit 1
 $TMUX2 new-session -d -s outer -x 80 -y 24 'sleep 100' || exit 1
 $TMUX2 set -g status off || exit 1
 $TMUX2 respawn-pane -k -t outer:0.0 "$TMUX attach -t inner" || exit 1
 sleep 1
 
+for side in left right; do
+	$TMUX set -g side-status "$side" || exit 1
+	if [ "$side" = left ]; then
+		column=3
+		text_column=17
+	else
+		column=69
+		text_column=51
+	fi
+	for status in off bottom top; do
+		offset=0
+		if [ "$status" = off ]; then
+			$TMUX set -g status off || exit 1
+		else
+			$TMUX set -g status 2 || exit 1
+			$TMUX set -g status-position "$status" || exit 1
+			[ "$status" = top ] && offset=2
+		fi
+		sleep 0.5
+		for window in 0 1; do
+			row=$((window + offset + 1))
+			check_menu "$column" "$row" "$window" \
+			    "$((row + 1)) $text_column"
+		done
+	done
+done
+
+# A noncurrent window's dimensions must not constrain the visible menu.
+$TMUX resize-window -t inner:1 -x 10 -y 5 || exit 1
+check_menu 69 4 1 '5 51'
+
+# The same target/display distinction applies to the horizontal status line.
+$TMUX set -g side-status off || exit 1
+$TMUX set -g status 2 || exit 1
+$TMUX set -g 'status-format[0]' \
+    '#[range=window|0]0:zero#[norange] #[range=window|1]1:one#[norange]' || \
+    exit 1
 for position in top bottom; do
 	$TMUX set -g status-position "$position" || exit 1
 	if [ "$position" = top ]; then
@@ -98,12 +141,8 @@ for position in top bottom; do
 		row=23
 	fi
 	sleep 0.5
-	check_menu 2 "$row" 0
-	check_menu 9 "$row" 1
+	check_menu 2 "$row" 0 ''
+	check_menu 9 "$row" 1 ''
 done
 
-# A noncurrent window's dimensions must not constrain the visible menu.
-$TMUX resize-window -t inner:1 -x 10 -y 5 || exit 1
-check_menu 9 23 1
-
 exit 0