[2831] more clarified when mapped setNamedAddress returns true.

src/lib/util/memory_segment_mapped.h

@@ -163,8 +163,11 @@ public:
     /// This implementation detects if \c addr is invalid (see the base class
     /// description) and throws \c MemorySegmentError in that case.
     ///
-    /// This version can actually return true (see also \c MemorySegmentLocal
-    /// version of the method).
+    /// This version of method should normally return false.  However,
+    /// it internally allocates memory in the segment for the name and
+    /// address to be stored, which can require segment extension, just like
+    /// allocate().  So it's possible to return true unlike
+    /// \c MemorySegmentLocal version of the method.
     ///
     /// This method cannot be called if the segment object is created in the
     /// read-only mode; in that case MemorySegmentError will be thrown.