diff --git a/docs/UsersManual.html b/docs/UsersManual.html
index 154cf86..a271dc3 100644
--- a/docs/UsersManual.html
+++ b/docs/UsersManual.html
@@ -922,6 +922,12 @@
 certain constructs (including __declspec and Microsoft-style asm statements).
 </p>
 
+<li>clang allows setting _MCS_VER with -fmsc-version=. It defaults to 1300 which
+is the same as Visual C/C++ 2003. Any number is supported and can greatly affect
+what Windows SDK and c++stdlib headers clang can compile. This option will be
+removed when clang supports the full set of MS extensions required for these
+headers.</li>
+
 <li>clang does not support the Microsoft extension where anonymous
 record members can be declared using user defined typedefs.</li>