saved_handler is a public interface:

This container allows completion handlers to be safely
suspended and resumed later, or destroyed.

doc/qbk/03_core/5_composed.qbk

@@ -97,6 +97,13 @@ composed operations:
     handler's associated allocator, benefiting from all handler memory
     management optimizations transparently.
 ]]
+[[
+    [link beast.ref.boost__beast__saved_handler `saved_handler`]
+][
+    This wrapper safely stores a completion handler so it may be invoked
+    later, allowing an implementation to "pause" an operation until some
+    condition is met.
+]]
 ]
 
 

doc/qbk/quickref.xml

@@ -203,6 +203,7 @@
             <member><link linkend="beast.ref.boost__beast__iequal">iequal</link></member>
             <member><link linkend="beast.ref.boost__beast__iless">iless</link></member>
             <member><link linkend="beast.ref.boost__beast__multi_buffer">multi_buffer</link></member>
+            <member><link linkend="beast.ref.boost__beast__saved_handler">saved_handler</link></member>
             <member><link linkend="beast.ref.boost__beast__span">span</link></member>
             <member><link linkend="beast.ref.boost__beast__static_buffer">static_buffer</link></member>
             <member><link linkend="beast.ref.boost__beast__static_buffer_base">static_buffer_base</link></member>