--- /dev/null
+/* -*- C++ -*- ------------------------------------------------------------
+
+Copyright (c) 2007 Jesse Anders and Demian Nave http://cmldev.net/
+
+The Configurable Math Library (CML) is distributed under the terms of the
+Boost Software License, v1.0 (see cml/LICENSE for details).
+
+ *-----------------------------------------------------------------------*/
+/** @file
+ * @brief
+ */
+
+#ifndef et_tags_h
+#define et_tags_h
+
+namespace cml {
+namespace et {
+
+/** Tag an expression as returning a scalar. */
+struct scalar_result_tag {};
+
+/** Tag an expression as returning a vector. */
+struct vector_result_tag {};
+
+/** Tag an expression as returning a matrix. */
+struct matrix_result_tag {};
+
+/** Tag an expression as returning a quaternion. */
+struct quaternion_result_tag {};
+
+/** Marker for unary expression ops. */
+struct unary_expression {};
+
+/** Marker for biary expression ops. */
+struct binary_expression {};
+
+/** Marker for expression tree operator nodes. */
+struct expr_node_tag {};
+
+/** Marker for expression tree terminals (leaves). */
+struct expr_leaf_tag {};
+
+/** Marker for assignable types. */
+struct assignable_tag {};
+
+/** Marker for assignable types. */
+struct not_assignable_tag {};
+
+} // namespace et
+} // namespace cml
+
+#endif
+
+// -------------------------------------------------------------------------
+// vim:ft=cpp