Index: clang/docs/ThreadSafetyAnalysis.rst
===================================================================
--- clang/docs/ThreadSafetyAnalysis.rst
+++ clang/docs/ThreadSafetyAnalysis.rst
@@ -447,10 +447,14 @@
 
 *Previously:*  ``ASSERT_EXCLUSIVE_LOCK``, ``ASSERT_SHARED_LOCK``
 
-These are attributes on a function or method that does a run-time test to see
-whether the calling thread holds the given capability.  The function is assumed
-to fail (no return) if the capability is not held.  See :ref:`mutexheader`,
-below, for example uses.
+These are attributes on a function or method which asserts the calling thread
+already holds the given capability, for example by performing a run-time test
+and terminating or throwing if the capability is not held.  Presence of this
+annotation causes the analysis to assume the capability is held at the point of
+the call. See :ref:`mutexheader`, below, for example uses.
+
+The given capability must be held on entry to the function, or the function is
+assumed to fail (no return).
 
 
 GUARDED_VAR and PT_GUARDED_VAR