diff --git a/demo/client.ts b/demo/client.ts
index f5903aa4..00d0bf67 100644
--- a/demo/client.ts
+++ b/demo/client.ts
@@ -1310,23 +1310,25 @@ function addVtButtons(): void {
   }
   const vtFragment = document.createDocumentFragment();
   const buttonSpecs: { [key: string]: { label: string, description: string, paramCount?: number }} = {
-    A:     { label: 'CUU ↑',    description: 'Cursor Up Ps Times' },
-    B:     { label: 'CUD ↓',    description: 'Cursor Down Ps Times' },
-    C:     { label: 'CUF →',    description: 'Cursor Forward Ps Times' },
-    D:     { label: 'CUB ←',    description: 'Cursor Backward Ps Times' },
-    E:     { label: 'CNL',      description: 'Cursor Next Line Ps Times' },
-    F:     { label: 'CPL',      description: 'Cursor Preceding Line Ps Times' },
-    G:     { label: 'CHA',      description: 'Cursor Character Absolute' },
-    H:     { label: 'CUP',      description: 'Cursor Position [row;column]', paramCount: 2 },
-    I:     { label: 'CHT',      description: 'Cursor Forward Tabulation Ps tab stops' },
-    J:     { label: 'ED',       description: 'Erase in Display' },
-    '?|J': { label: 'DECSED',   description: 'Erase in Display' },
-    K:     { label: 'EL',       description: 'Erase in Line' },
-    '?|K': { label: 'DECSEL',   description: 'Erase in Line' },
-    L:     { label: 'IL',       description: 'Insert Ps Line(s)' },
-    M:     { label: 'DL',       description: 'Delete Ps Line(s)' },
-    P:     { label: 'DCH',      description: 'Delete Ps Character(s)' },
-    ' q':  { label: 'DECSCUSR', description: 'Set Cursor Style', paramCount: 1 }
+    A:         { label: 'CUU ↑',    description: 'Cursor Up Ps Times' },
+    B:         { label: 'CUD ↓',    description: 'Cursor Down Ps Times' },
+    C:         { label: 'CUF →',    description: 'Cursor Forward Ps Times' },
+    D:         { label: 'CUB ←',    description: 'Cursor Backward Ps Times' },
+    E:         { label: 'CNL',      description: 'Cursor Next Line Ps Times' },
+    F:         { label: 'CPL',      description: 'Cursor Preceding Line Ps Times' },
+    G:         { label: 'CHA',      description: 'Cursor Character Absolute' },
+    H:         { label: 'CUP',      description: 'Cursor Position [row;column]', paramCount: 2 },
+    I:         { label: 'CHT',      description: 'Cursor Forward Tabulation Ps tab stops' },
+    J:         { label: 'ED',       description: 'Erase in Display' },
+    '?|J':     { label: 'DECSED',   description: 'Erase in Display' },
+    K:         { label: 'EL',       description: 'Erase in Line' },
+    '?|K':     { label: 'DECSEL',   description: 'Erase in Line' },
+    L:         { label: 'IL',       description: 'Insert Ps Line(s)' },
+    M:         { label: 'DL',       description: 'Delete Ps Line(s)' },
+    P:         { label: 'DCH',      description: 'Delete Ps Character(s)' },
+    ' q':      { label: 'DECSCUSR', description: 'Set Cursor Style' },
+    '?2026h':  { label: 'BSU',      description: 'Begin synchronized update', paramCount: 0 },
+    '?2026l':  { label: 'ESU',      description: 'End synchronized update', paramCount: 0 }
   };
   for (const s of Object.keys(buttonSpecs)) {
     const spec = buttonSpecs[s];