diff --git a/docs/InternalsManual.html b/docs/InternalsManual.html
index 6df26db..2eee5c2 100644
--- a/docs/InternalsManual.html
+++ b/docs/InternalsManual.html
@@ -1682,6 +1682,7 @@
     floating-point literal.</li>
 <li><b><tt>__builtin_abs,copysign,..</tt></b>: These are constant folded as
     general constant expressions.</li>
+<li><b><tt>__builtin_strlen</tt></b> and <b><tt>strlen</tt></b>: These are constant folded as integer constant expressions if the argument is a string literal.</li>
 </ul>