diff --git a/src/terminal.ts b/src/terminal.ts
index 154d6f8..87e3394 100644
--- a/src/terminal.ts
+++ b/src/terminal.ts
@@ -46,7 +46,16 @@ export function serializeAsHTML(session: TerminalSession): string {
 /**
  * Trim empty trailing rows and trailing whitespace from xterm HTML output.
  *
- * Structure: <html><body><!--StartFragment--><pre><div style='...'><div><span>...</span></div>...</div></pre><!--EndFragment--></body></html>
+ * WARNING: This function depends on xterm's specific HTML structure from serializeAsHTML().
+ * If xterm changes their HTML format, this will need updating. Consider filing an issue
+ * with xterm to add a native trimEmpty option.
+ *
+ * Current structure expected:
+ * - Outer: <pre class="xterm-screen">
+ * - Rows: <div style="..."><div><span>content</span></div></div>
+ * - Empty cells: &nbsp; or plain spaces
+ *
+ * Full structure: <html><body><!--StartFragment--><pre><div style='...'><div><span>...</span></div>...</div></pre><!--EndFragment--></body></html>
  * Each row is: <div><span>content</span></div>
  */
 function trimHtmlOutput(html: string): string {
