diff --git a/docs/UsersManual.html b/docs/UsersManual.html
index def16c1..e7072da 100644
--- a/docs/UsersManual.html
+++ b/docs/UsersManual.html
@@ -600,6 +600,12 @@
 to implement, two, the extension is completely undocumented, and three, the
 extension appears to be very rarely used.</p>
 
+<p>clang does not support duplicate definitions of a function where one is
+inline. This complicates clients of the AST which normally can expect there is
+at most one definition for each function. Source code using this feature should
+be changed to define the inline and out-of-line definitions in separate
+translation units.</p>
+
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 <h3 id="c_ms">Microsoft extensions</h3>
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