Beast documentation work

include/beast/http/streambuf_body.hpp

@@ -23,8 +23,13 @@ namespace http {
 template<class Streambuf>
 struct basic_streambuf_body
 {
+    /// The type of the `message::body` member
     using value_type = Streambuf;
 
+#if GENERATING_DOCS
+private:
+#endif
+
     class reader
     {
         value_type& sb_;