diff --git a/libcxx/docs/UsingLibcxx.rst b/libcxx/docs/UsingLibcxx.rst
--- a/libcxx/docs/UsingLibcxx.rst
+++ b/libcxx/docs/UsingLibcxx.rst
@@ -346,3 +346,19 @@
 * ``unique``
 * ``upper_bound``
 * ``lock_guard``'s constructors
+
+.. _noexcept extension:
+
+Extended applications of ``noexcept``
+------------------------------------------
+
+As of version 14 libc++ will mark functions that do not throw (i.e.,
+"Throws: nothing" as ``noexcept``). This means that functions will not
+report precondition violations by throwing and user-provided functions,
+such as custom predicates or custom traits, which throw will not be
+propagated up to the caller (unless specified otherwise by the standard).
+
+Before version 14, libc++ did not specify whether a function that did not
+throw would be marked as ``noexcept``, so users should not rely on any
+non-throwing functions to be marked ``noexcept`` (unless the standard
+specifies it).
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