--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/graal/com.oracle.truffle.api/src/com/oracle/truffle/api/instrument/PhylumTag.java	Sun Apr 20 20:37:27 2014 -0700
@@ -0,0 +1,70 @@
+/*
+ * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+package com.oracle.truffle.api.instrument;
+
+/**
+ * Program element "tags" that define user-visible behavior for debugging and other simple tools.
+ * These categories (<em>phyla</em>) should correspond to program structures that are meaningful to
+ * a guest language programmer.
+ * <p>
+ * An untagged Truffle node should be understood as an artifact of the guest language implementation
+ * and should not be visible to the user of a guest language programming tool. Nodes may also have
+ * more than one tag, for example a variable assignment that is also a statement. Finally, the
+ * assignment of tags to nodes could depending on the use-case of whatever tool is using them.
+ * <p>
+ * This is a somewhat language-agnostic set of phyla, suitable for conventional imperative
+ * languages, and is being developed incrementally.
+ * <p>
+ * The need for alternative sets of tags is likely to arise, perhaps for other families of languages
+ * (for example for mostly expression-oriented languages) or even for specific languages.
+ * <p>
+ * These are listed alphabetically so that listing from some collection classes will come out in
+ * that order.
+ * <p>
+ * <strong>Disclaimer:</strong> experimental interface under development.
+ */
+public enum PhylumTag {
+
+    /**
+     * Marker for a variable assignment.
+     */
+    ASSIGNMENT,
+
+    /**
+     * Marker for a call site.
+     */
+    CALL,
+
+    /**
+     * Marker for a location where a guest language exception is about to be thrown.
+     */
+    THROW,
+
+    /**
+     * Marker for a location where ordinary "stepping" should halt.
+     */
+    STATEMENT;
+
+}