diff --git a/layout-custom.c b/layout-custom.c
index f801108ec..6164dc924 100644
--- a/layout-custom.c
+++ b/layout-custom.c
@@ -126,8 +126,7 @@ layout_append_geometry(char *buf, size_t len, u_int sx, u_int sy, int xoff,
 		y = -(long long)yoff;
 	} else
 		y = yoff;
-	return (xsnprintf(buf, len, "%ux%u%s%llu%s%llu", sx, sy, xs, x,
-	    ys, y));
+	return (xsnprintf(buf, len, "%ux%u%s%llu%s%llu", sx, sy, xs, x, ys, y));
 }
 
 /* Dump layout as a string. */
diff --git a/regress/layout-custom.sh b/regress/layout-custom.sh
index a9e1bd821..3846dca64 100755
--- a/regress/layout-custom.sh
+++ b/regress/layout-custom.sh
@@ -27,6 +27,7 @@ must_fail()
 }
 
 $TMUX kill-server 2>/dev/null
+sleep 0.5
 $TMUX new-session -d -x 80 -y 24 || exit 1
 $TMUX split-window -h || fail "split-window failed"
 
@@ -47,6 +48,34 @@ must_equal "$($TMUX display-message -p '#{window_layout}')" "$layout"
 must_fail $TMUX select-layout \
     '0000,80x24+0+0{%0,0:39x24+0+0;%1,1:40x24+40+0}'
 
+# Top-bottom containers are accepted in both current and legacy formats.
+topbottom='081e,80x24+0+0[%0,0:80x11+0+0;%1,1:80x12+0+12]'
+$TMUX select-layout "$topbottom" || fail "top-bottom layout was rejected"
+must_equal "$($TMUX display-message -p '#{window_layout}')" "$topbottom"
+must_equal "$($TMUX list-panes -F '#{pane_width}x#{pane_height},#{pane_left},#{pane_top}')" \
+    '80x11,0,0
+80x12,0,12'
+$TMUX select-layout '80x24,0,0[80x11,0,0,0,80x12,0,12,1]' || \
+    fail "legacy top-bottom layout was rejected"
+must_equal "$($TMUX display-message -p '#{window_layout}')" "$topbottom"
+$TMUX select-layout "$layout" || fail "layout could not be restored"
+
+# Exercise select-layout command paths around custom layout parsing.
+$TMUX select-layout even-vertical || fail "named layout failed"
+$TMUX select-layout -n || fail "next layout failed"
+$TMUX select-layout -p || fail "previous layout failed"
+$TMUX select-layout -o || fail "old layout failed"
+$TMUX select-layout -E || fail "spread layout failed"
+$TMUX select-layout "$layout" || fail "layout could not be restored"
+
+# A command-zoomed tiled pane emits the z flag without changing its saved
+# tiled geometry.
+$TMUX resize-pane -t %0 -Z || fail "tiled zoom failed"
+must_equal "$($TMUX display-message -p '#{window_layout}')" \
+    '8e46,80x24+0+0{%0,0:39x24+0+0:z;%1,1:40x24+40+0}'
+$TMUX resize-pane -t %0 -Z || fail "tiled unzoom failed"
+$TMUX select-layout "$layout" || fail "layout could not be restored"
+
 # Whitespace and newlines between tokens do not affect the checksum.
 indented='93fc,
   80x24 +0 +0 {
@@ -109,6 +138,7 @@ must_fail $TMUX select-layout \
 # assigns the remaining cells in tree order. A target with more panes fails.
 fewer='80x24+0+0{%100,1:26x24+0+0;%101,2:26x24+27+0;%102,0:26x24+54+0:z}'
 $TMUX select-layout "$fewer" || fail "surplus current cells were not removed"
+must_equal "$($TMUX display-message -p '#{window_panes}')" 2
 must_equal "$($TMUX display-message -p -t %0 '#{pane_left},#{pane_width}')" \
     '0,26'
 must_equal "$($TMUX display-message -p -t %1 '#{pane_left},#{pane_width}')" \
@@ -123,15 +153,40 @@ esac
 must_fail $TMUX select-layout \
     '80x24+0+0{%100,0:39x24+0+0;%101,1:20x24+40+0;%102,2:19x10+61+0}'
 must_fail $TMUX select-layout '%100,0:80x24+0+0'
+must_fail $TMUX select-layout '80x24,0,0,0'
 $TMUX select-layout "$legacy" || fail "legacy layout could not be restored"
 
-# Mixed legacy and new separators, duplicate z-indices and unknown flags fail.
+# Mixed legacy and new syntax, malformed containers, duplicate z-indices,
+# non-contiguous z-indices, invalid z-ordering and unknown flags fail.
 must_fail $TMUX select-layout \
     '93ed,80x24+0+0{%0,0:39x24+0+0,%1,1:40x24+40+0}'
+must_fail $TMUX select-layout \
+    '80x24,0,0{39x24,0,0,0;%1,1:40x24+40+0}'
+must_fail $TMUX select-layout '80x24+0+0{}'
+must_fail $TMUX select-layout \
+    '80x24+0+0{%0,0:39x24+0+0;}'
+must_fail $TMUX select-layout \
+    '80x24+0+0{%0,0:39x24+0+0|%1,1:40x24+40+0}'
 must_fail $TMUX select-layout \
     '93ec,80x24+0+0{%0,0:39x24+0+0;%1,0:40x24+40+0}'
+must_fail $TMUX select-layout \
+    '80x24+0+0{%0,0:39x24+0+0;%1,2:40x24+40+0}'
+must_fail $TMUX select-layout \
+    '80x24+0+0{%0,0:39x24+0+0;%1,1:40x24+40+0:f}'
+must_fail $TMUX select-layout \
+    '80x24+0+0{%0,0:38x24+0+0;%1,1:40x24+39+0}'
 must_fail $TMUX select-layout \
     '0e42,80x24+0+0{%0,0:39x24+0+0:q;%1,1:40x24+40+0}'
+must_fail $TMUX select-layout \
+    '80x24+0+0{%0,0:39x24+0+0:ff;%1,1:40x24+40+0}'
+must_fail $TMUX select-layout \
+    '80x24+0+0{%0,0:39x24+0+0:hh;%1,1:40x24+40+0}'
+must_fail $TMUX select-layout \
+    '80x24+0+0{%0,0:39x24+0+0:zz;%1,1:40x24+40+0}'
+must_fail $TMUX select-layout \
+    '80x24+0+0{%0,0:39x24+0+0:z;%1,1:40x24+40+0:z}'
+must_fail $TMUX select-layout \
+    '80x24,0,0{39x24,0,0,0,40x24,40,0,}'
 
 # Truncated and overflowing values must fail without terminating the server.
 must_fail $TMUX select-layout '0000,'
@@ -143,6 +198,23 @@ must_fail $TMUX select-layout \
     '80x24+0+0{%0,0:39x24+2147483647+0;%1,1:40x24+40+0}'
 must_fail $TMUX select-layout \
     '80x24+0+0{%0,0:39x24+0+0;%1,1:40x24+-10001+0}'
+must_fail $TMUX select-layout \
+    '80x24-1+0{%0,0:39x24+0+0;%1,1:40x24+40+0}'
+must_fail $TMUX select-layout \
+    '80x24+0+0{%0,0:39x24-1+0;%1,1:40x24+40+0}'
+must_fail $TMUX select-layout \
+    '80x24+0+0{%0,0:39x24+;%1,1:40x24+40+0}'
+must_fail $TMUX select-layout \
+    '80x24+0+0{%0,0:39x24+0+;%1,1:40x24+40+0}'
+must_fail $TMUX select-layout \
+    '80x24+0+0{%0,0:39x24++ +0;%1,1:40x24+40+0}'
+long='80x24+0+0{%0,0:39x24+0+0;%1,1:40x24+40+0}'
+i=0
+while [ $i -lt 9000 ]; do
+	long="${long}x"
+	i=$((i + 1))
+done
+must_fail $TMUX select-layout "$long"
 $TMUX list-windows >/dev/null || fail "server exited after invalid layouts"
 
 # Invalid custom layouts must not unzoom the target window.
@@ -154,7 +226,11 @@ $TMUX resize-pane -t %0 -Z || fail "unzoom failed"
 
 # The parser accepts its maximum nesting depth and safely rejects one more.
 $TMUX kill-server 2>/dev/null
+sleep 0.5
 $TMUX new-session -d -x 80 -y 24 || exit 1
+legacy_negative='a9af,%0,0:20x8+0+0'
+$TMUX select-layout '20x8,-10,-20,0' || fail "legacy negative layout failed"
+must_equal "$($TMUX display-message -p '#{window_layout}')" "$legacy_negative"
 deep='%0,0:1x1+0+0'
 i=1
 while [ $i -lt 64 ]; do
@@ -167,8 +243,20 @@ must_fail $TMUX select-layout "1x1+0+0{$deep}"
 # X-style geometry supports right/bottom-relative offsets, absolute negative
 # offsets, doubled plus signs, and omitted positions.
 $TMUX kill-server 2>/dev/null
+sleep 0.5
 $TMUX new-session -d -x 120 -y 40 || exit 1
 $TMUX new-pane -d -x 20 -y 8 'sleep 100' || fail "floating pane failed"
+
+# A real floating pane moved partly outside the window emits absolute negative
+# offsets in canonical X-style form.
+$TMUX move-pane -t %1 -X -10 -Y -20 || fail "negative move-pane failed"
+must_equal "$($TMUX display-message -p -t %1 '#{pane_left},#{pane_top},#{pane_width},#{pane_height}')" \
+    '-9,-19,18,6'
+case "$($TMUX display-message -p '#{window_layout}')" in
+*'%1,0:18x6+-9+-19:f'*) ;;
+*) fail "negative floating pane was not serialized with +- offsets" ;;
+esac
+
 relative='1442,120x40+0+0{%0,1:120x40+0+0;%1,0:30x10-10-20:f}'
 $TMUX select-layout "$relative" || fail "relative geometry was rejected"
 must_equal "$($TMUX display-message -p -t %1 '#{pane_left},#{pane_top}')" \
@@ -176,12 +264,32 @@ must_equal "$($TMUX display-message -p -t %1 '#{pane_left},#{pane_top}')" \
 must_equal "$($TMUX display-message -p '#{window_layout}')" \
     '0041,120x40+0+0{%0,1:120x40+0+0;%1,0:30x10+80+10:f}'
 
+bottomright='120x40+0+0{%0,1:120x40+0+0;%1,0:30x10-0-0:f}'
+$TMUX select-layout "$bottomright" || fail "bottom-right geometry failed"
+must_equal "$($TMUX display-message -p -t %1 '#{pane_left},#{pane_top}')" \
+    '90,30'
+must_equal "$($TMUX display-message -p '#{window_layout}')" \
+    '2242,120x40+0+0{%0,1:120x40+0+0;%1,0:30x10+90+30:f}'
+
 absolute='3a22,120x40+0+0{%0,1:120x40+0+0;%1,0:20x8+-10+-20:f}'
 $TMUX select-layout "$absolute" || fail "absolute negative geometry failed"
 must_equal "$($TMUX display-message -p -t %1 '#{pane_left},#{pane_top}')" \
     '-10,-20'
 must_equal "$($TMUX display-message -p '#{window_layout}')" "$absolute"
 
+hiddenfloat='120x40+0+0{%0,1:120x40+0+0;%1,0:20x8+-10+-20:fh}'
+$TMUX select-layout "$hiddenfloat" || fail "hidden floating layout failed"
+must_equal "$($TMUX display-message -p -t %1 '#{pane_left},#{pane_top},#{pane_width},#{pane_height}')" \
+    '-10,-20,20,8'
+must_equal "$($TMUX display-message -p '#{window_layout}')" \
+    '9d83,120x40+0+0{%0,1:120x40+0+0;%1,0:20x8+-10+-20:fh}'
+must_fail $TMUX select-layout \
+    '120x40+0+0{%0,1:120x40+0+0;%1,0:20x8+-10+-20:fhz}'
+must_equal "$($TMUX display-message -p '#{window_layout}')" \
+    '9d83,120x40+0+0{%0,1:120x40+0+0;%1,0:20x8+-10+-20:fh}'
+must_fail $TMUX select-layout \
+    '120x40+0+0{%0,1:120x40+0+0;%1,0:10000x8-10000+0:f}'
+
 defaults='fcb6,120x40{%0,1:120x40;%1,0:30x10++80+10:f}'
 $TMUX select-layout "$defaults" || fail "default or doubled offsets failed"
 must_equal "$($TMUX display-message -p '#{window_layout}')" \
@@ -193,6 +301,7 @@ must_equal "$($TMUX display-message -p '#{window_layout}')" \
     '5fb9,120x40+0+0{%0,1:120x40+0+0;%1,0:30x10+80+0:f}'
 
 $TMUX kill-server 2>/dev/null
+sleep 0.5
 $TMUX new-session -d -x 80 -y 24 || exit 1
 $TMUX split-window -h || fail "split-window failed"
 
@@ -212,11 +321,14 @@ before=$($TMUX display-message -p -t @0 '#{window_width}x#{window_height}')
 must_fail $TMUX select-layout "@0:$reported@1:0000,"
 must_equal "$($TMUX display-message -p -t @0 '#{window_width}x#{window_height}')" \
     "$before"
+must_fail $TMUX select-layout '@0'
+must_fail $TMUX select-layout '@0:'
 must_fail $TMUX select-layout "@0:$legacy@0:$legacy"
 must_fail $TMUX select-layout "@999999:$legacy"
 
 # Add floating panes and verify exact z-order, semicolon output and zoom state.
 $TMUX kill-server 2>/dev/null
+sleep 0.5
 $TMUX new-session -d -x 120 -y 40 || exit 1
 $TMUX split-window -h || fail "split-window failed"
 $TMUX new-pane -d -x 30 -y 10 -X 10 -Y 5 'sleep 100' || \
@@ -225,6 +337,8 @@ $TMUX new-pane -d -x 24 -y 8 -X 50 -Y 12 'sleep 100' || \
     fail "second floating pane failed"
 
 layout=$($TMUX display-message -p '#{window_layout}')
+must_equal "$layout" \
+    'a6f2,120x40+0+0{%0,2:60x40+0+0;%1,3:59x40+61+0;%3,0:22x6+51+13:f;%2,1:28x8+11+6:f}'
 case "$layout" in
 *'<'*|*'>'*) fail "obsolete floating delimiters were emitted" ;;
 esac