--- /dev/null
+// Boost.Bimap
+//
+// Copyright (c) 2006-2007 Matias Capeletto
+//
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+/// \file relation/member_at.hpp
+/// \brief Defines the tags for the member_at::side idiom
+
+#ifndef BOOST_BIMAP_RELATION_MEMBER_AT_HPP
+#define BOOST_BIMAP_RELATION_MEMBER_AT_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER>=1200)
+#pragma once
+#endif
+
+#include <boost/config.hpp>
+
+namespace boost {
+namespace bimaps {
+namespace relation {
+
+/// \brief member_at::side idiom to access relation values and types using metaprogramming.
+/**
+
+This tags are used to specify which member you want to acces when using a metafunction over
+a symmetrical type. The idea is to be able to write code like:
+
+\code
+result_of::get<member_at::left,relation>::type data = get<member_at::left>(rel);
+\endcode
+
+The relation class supports this idiom even when the elements are tagged. This is useful
+because a user can decide to start tagging in any moment of the development.
+
+See also member_with_tag, is_tag_of_member_at_left, is_tag_of_member_at_right, get
+value_type_of, pair_by, pair_type_by.
+
+\ingroup relation_group
+ **/
+namespace member_at {
+
+ /// \brief Member at left tag
+ /**
+ See also member_at, rigth.
+ **/
+
+ struct left {};
+
+ /// \brief Member at right tag
+ /**
+ See also member_at, left.
+ **/
+
+ struct right {};
+
+ /// \brief Member info tag
+ /**
+ See also member_at, left, right.
+ **/
+
+ struct info {};
+
+}
+
+} // namespace relation
+} // namespace bimaps
+} // namespace boost
+
+#endif // BOOST_BIMAP_RELATION_MEMBER_AT_HPP