diff --git a/build.xml b/build.xml
index a3a9e6c8a..62a36646d 100644
--- a/build.xml
+++ b/build.xml
@@ -20,6 +20,7 @@
     <fileset dir="${deploy.dir}/lib" includes="**/*.jar"/>
   </path>
 
+
   <!-- generates fields for persistent record classes -->
   <target name="genrecord" depends="prepare">
     <taskdef name="grecord" classname="com.samskivert.jdbc.depot.tools.GenRecordTask"
@@ -171,9 +172,14 @@
   <target name="checkaslib">
     <condition property="no_build_aslib"><or>
       <not><available file="${flexsdk.dir}/lib/compc.jar"/></not>
-      <uptodate targetfile="${deploy.dir}/${lib.name}lib.swc">
-        <srcfiles dir="src/as" includes="**/*.as"/>
-      </uptodate>
+      <and>
+        <uptodate targetfile="${deploy.dir}/${lib.name}lib.swc">
+          <srcfiles dir="src/as" includes="**/*.as"/>
+        </uptodate>
+        <uptodate targetfile="${deploy.dir}/${lib.name}lib.abc">
+          <srcfiles dir="src/as" includes="**/*.as"/>
+        </uptodate>
+      </and>
     </or></condition>
   </target>
 
@@ -185,6 +191,9 @@
         <filter token="lib_name_dir" value="${lib.name}"/>
       </filterset>
     </copy>
+    <copy file="src/as/com/threerings/util/env/Environment.as-fp" 
+          tofile="src/as/com/threerings/util/env/Environment.as"/>
+
     <java jar="${flexsdk.dir}/lib/compc.jar" fork="true" failonerror="true">
       <arg value="-load-config"/>
       <arg value="${deploy.dir}/aslib-config.xml"/>
@@ -195,6 +204,32 @@
       <arg value="${deploy.dir}/${lib.name}lib.swc"/>
     </java>
     <delete file="${deploy.dir}/aslib-config.xml"/>
+
+    <copy file="src/as/com/threerings/util/env/Environment.as-tm"
+          tofile="src/as/com/threerings/util/env/Environment.as"/>
+    <loadfile property="ascfiles" srcFile="etc/asc-files.txt">
+      <filterchain>
+        <prefixlines prefix="src/as/"/>
+        <tokenfilter delimOutput=" "/>
+      </filterchain>
+    </loadfile>
+    <java classname="macromedia.asc.embedding.ScriptCompiler" fork="true" failonerror="true">
+      <classpath>
+        <fileset dir="lib" includes="asc.jar"/>
+      </classpath>
+      <arg value="-AS3"/>
+      <arg value="-strict"/>
+      <arg value="-import"/>
+      <arg value="lib/builtin.abc"/>
+      <arg value="-import"/>
+      <arg value="lib/thane.abc"/>
+      <arg value="-outdir"/>
+      <arg value="${deploy.dir}"/>
+      <arg value="-out"/>
+      <arg value="${lib.name}lib"/>
+      <arg line="${ascfiles}"/>
+    </java>
+    <delete file="src/as/com/threerings/util/env/Environment.as"/>
   </target>
 
   <!-- build the native libraries -->
diff --git a/etc/asc-files.txt b/etc/asc-files.txt
new file mode 100644
index 000000000..4333c4ea7
--- /dev/null
+++ b/etc/asc-files.txt
@@ -0,0 +1,139 @@
+com/threerings/util/ArrayIterator.as
+com/threerings/util/ArrayUtil.as
+com/threerings/util/Byte.as
+com/threerings/util/ClassUtil.as
+com/threerings/util/Cloneable.as
+com/threerings/util/Comparable.as
+com/threerings/util/Comparators.as
+com/threerings/util/Equalable.as
+com/threerings/util/env/Environment.as
+com/threerings/util/Float.as
+com/threerings/util/HashMap.as
+com/threerings/util/Hashable.as
+com/threerings/util/Integer.as
+com/threerings/util/Iterator.as
+com/threerings/util/Log.as
+com/threerings/util/LogTarget.as
+com/threerings/util/Long.as
+com/threerings/util/Map.as
+com/threerings/util/MethodQueue.as
+com/threerings/util/Name.as
+com/threerings/util/ObserverList.as
+com/threerings/util/Random.as
+com/threerings/util/ResultListener.as
+com/threerings/util/Short.as
+com/threerings/util/StreamableArrayList.as
+com/threerings/util/StreamableHashMap.as
+com/threerings/util/StringBuilder.as
+com/threerings/util/StringUtil.as
+com/threerings/util/Util.as
+com/threerings/util/Wrapped.as
+com/threerings/io/ArrayMask.as
+com/threerings/io/ClassMapping.as
+com/threerings/io/FrameAvailableEvent.as
+com/threerings/io/FrameReader.as
+com/threerings/io/ObjectInputStream.as
+com/threerings/io/ObjectOutputStream.as
+com/threerings/io/SimpleStreamableObject.as
+com/threerings/io/Streamable.as
+com/threerings/io/Streamer.as
+com/threerings/io/streamers/ArrayStreamer.as
+com/threerings/io/streamers/ByteArrayStreamer.as
+com/threerings/io/streamers/ByteStreamer.as
+com/threerings/io/streamers/FloatStreamer.as
+com/threerings/io/streamers/IntegerStreamer.as
+com/threerings/io/streamers/LongStreamer.as
+com/threerings/io/streamers/NumberStreamer.as
+com/threerings/io/streamers/ShortStreamer.as
+com/threerings/io/streamers/StringStreamer.as
+com/threerings/io/Translations.as
+com/threerings/io/TypedArray.as
+com/threerings/presents/client/BasicDirector.as
+com/threerings/presents/client/Client.as
+com/threerings/presents/client/ClientAdapter.as
+com/threerings/presents/client/ClientDObjectMgr.as
+com/threerings/presents/client/ClientEvent.as
+com/threerings/presents/client/ClientObserver.as
+com/threerings/presents/client/Communicator.as
+com/threerings/presents/client/ConfirmAdapter.as
+com/threerings/presents/client/InvocationAdapter.as
+com/threerings/presents/client/InvocationDecoder.as
+com/threerings/presents/client/InvocationDirector.as
+com/threerings/presents/client/InvocationReceiver.as
+com/threerings/presents/client/InvocationReceiver_Registration.as
+com/threerings/presents/client/InvocationService.as
+com/threerings/presents/client/InvocationService_ConfirmListener.as
+com/threerings/presents/client/InvocationService_InvocationListener.as
+com/threerings/presents/client/InvocationService_ResultListener.as
+com/threerings/presents/client/LogonError.as
+com/threerings/presents/client/ResultWrapper.as
+com/threerings/presents/client/ServerSwitcher.as
+com/threerings/presents/client/SessionObserver.as
+com/threerings/presents/client/TimeBaseService.as
+com/threerings/presents/client/TimeBaseService_GotTimeBaseListener.as
+com/threerings/presents/data/AuthCodes.as
+com/threerings/presents/data/ClientObject.as
+com/threerings/presents/data/ConMgrStats.as
+com/threerings/presents/data/InvocationCodes.as
+com/threerings/presents/data/InvocationMarshaller.as
+com/threerings/presents/data/InvocationMarshaller_ConfirmMarshaller.as
+com/threerings/presents/data/InvocationMarshaller_ListenerMarshaller.as
+com/threerings/presents/data/InvocationMarshaller_ResultMarshaller.as
+com/threerings/presents/data/TimeBaseMarshaller.as
+com/threerings/presents/data/TimeBaseMarshaller_GotTimeBaseMarshaller.as
+com/threerings/presents/dobj/AttributeChangeListener.as
+com/threerings/presents/dobj/AttributeChangedEvent.as
+com/threerings/presents/dobj/ChangeListener.as
+com/threerings/presents/dobj/CompoundEvent.as
+com/threerings/presents/dobj/DEvent.as
+com/threerings/presents/dobj/DObject.as
+com/threerings/presents/dobj/DObjectManager.as
+com/threerings/presents/dobj/DSet.as
+com/threerings/presents/dobj/DSet_Entry.as
+com/threerings/presents/dobj/DummyEntry.as
+com/threerings/presents/dobj/ElementUpdateListener.as
+com/threerings/presents/dobj/ElementUpdatedEvent.as
+com/threerings/presents/dobj/EntryAddedEvent.as
+com/threerings/presents/dobj/EntryRemovedEvent.as
+com/threerings/presents/dobj/EntryUpdatedEvent.as
+com/threerings/presents/dobj/EventListener.as
+com/threerings/presents/dobj/InvocationNotificationEvent.as
+com/threerings/presents/dobj/InvocationRequestEvent.as
+com/threerings/presents/dobj/InvocationResponseEvent.as
+com/threerings/presents/dobj/MessageAdapter.as
+com/threerings/presents/dobj/MessageEvent.as
+com/threerings/presents/dobj/MessageListener.as
+com/threerings/presents/dobj/NamedEvent.as
+com/threerings/presents/dobj/ObjectAccessError.as
+com/threerings/presents/dobj/ObjectAddedEvent.as
+com/threerings/presents/dobj/ObjectDeathListener.as
+com/threerings/presents/dobj/ObjectDestroyedEvent.as
+com/threerings/presents/dobj/ObjectRemovedEvent.as
+com/threerings/presents/dobj/OidList.as
+com/threerings/presents/dobj/OidListListener.as
+com/threerings/presents/dobj/ServerMessageEvent.as
+com/threerings/presents/dobj/SetAdapter.as
+com/threerings/presents/dobj/SetListener.as
+com/threerings/presents/dobj/Subscriber.as
+com/threerings/presents/dobj/SubscriberAdapter.as
+com/threerings/presents/net/AuthRequest.as
+com/threerings/presents/net/AuthResponse.as
+com/threerings/presents/net/AuthResponseData.as
+com/threerings/presents/net/BootstrapData.as
+com/threerings/presents/net/BootstrapNotification.as
+com/threerings/presents/net/Credentials.as
+com/threerings/presents/net/DownstreamMessage.as
+com/threerings/presents/net/EventNotification.as
+com/threerings/presents/net/FailureResponse.as
+com/threerings/presents/net/ForwardEventRequest.as
+com/threerings/presents/net/LogoffRequest.as
+com/threerings/presents/net/ObjectResponse.as
+com/threerings/presents/net/PingRequest.as
+com/threerings/presents/net/PongResponse.as
+com/threerings/presents/net/SubscribeRequest.as
+com/threerings/presents/net/UnsubscribeRequest.as
+com/threerings/presents/net/UnsubscribeResponse.as
+com/threerings/presents/net/UpstreamMessage.as
+com/threerings/presents/net/UsernamePasswordCreds.as
+com/threerings/presents/util/PresentsContext.as
+com/threerings/presents/util/SafeSubscriber.as
diff --git a/lib/asc.jar b/lib/asc.jar
new file mode 100644
index 000000000..6a99da645
Binary files /dev/null and b/lib/asc.jar differ
diff --git a/lib/builtin.abc b/lib/builtin.abc
new file mode 100644
index 000000000..5450b3b70
Binary files /dev/null and b/lib/builtin.abc differ
diff --git a/lib/thane.abc b/lib/thane.abc
new file mode 100644
index 000000000..7a007b5e7
Binary files /dev/null and b/lib/thane.abc differ
diff --git a/src/as/com/threerings/util/ClassUtil.as b/src/as/com/threerings/util/ClassUtil.as
index 7c0d07477..97bad3932 100644
--- a/src/as/com/threerings/util/ClassUtil.as
+++ b/src/as/com/threerings/util/ClassUtil.as
@@ -25,6 +25,8 @@ import flash.utils.describeType;
 import flash.utils.getQualifiedClassName;
 import flash.utils.getDefinitionByName;
 
+import com.threerings.util.env.Environment;
+
 public class ClassUtil
 {
     /**
@@ -111,39 +113,9 @@ public class ClassUtil
      *     var s :Streamable = (new someClass() as Streamable);
      * </code>
      */
-    public static function isAssignableAs (
-            asClass :Class, srcClass :Class) :Boolean
+    public static function isAssignableAs (asClass :Class, srcClass :Class) :Boolean
     {
-        if (asClass == srcClass) {
-            return true;
-
-        // if not the same class and srcClass is Object, we're done
-        } else if (srcClass == Object) {
-            return false;
-        }
-
-        // ok, let's introspect on the class and see what we've got.
-        var typeInfo :XMLList = describeType(srcClass).child("factory");
-
-        // See which classes we extend.
-        var exts :XMLList = typeInfo.child("extendsClass").attribute("type");
-        var type :String;
-        for each (type in exts) {
-            if (asClass == getClassByName(type)) {
-                return true;
-            }
-        }
-
-        // See which interfaces we implement.
-        var imps :XMLList = typeInfo.child("implementsInterface")
-            .attribute("type");
-        for each (type in imps) {
-            if (asClass == getClassByName(type)) {
-                return true;
-            }
-        }
-
-        return false;
+        return Environment.isAssignableAs(asClass, srcClass);
     }
 }
 }
diff --git a/src/as/com/threerings/util/StringUtil.as b/src/as/com/threerings/util/StringUtil.as
index c9b17a607..6935977a5 100644
--- a/src/as/com/threerings/util/StringUtil.as
+++ b/src/as/com/threerings/util/StringUtil.as
@@ -22,7 +22,8 @@
 package com.threerings.util {
 
 import flash.utils.ByteArray;
-import flash.utils.describeType; // function import
+
+import com.threerings.util.env.Environment;
 
 public class StringUtil
 {
@@ -318,9 +319,8 @@ public class StringUtil
      */
     public static function fieldsToString (buf :StringBuilder, obj :Object) :void
     {
-        var desc :XML = describeType(obj);
         var appended :Boolean = false;
-        for each (var varName :String in desc..variable.@name) {
+        for each (var varName :String in Environment.enumerateFields(obj)) {
             if (appended) {
                 buf.append(", ");
             }
diff --git a/src/as/com/threerings/util/env/Environment.as-fp b/src/as/com/threerings/util/env/Environment.as-fp
new file mode 100644
index 000000000..49e926752
--- /dev/null
+++ b/src/as/com/threerings/util/env/Environment.as-fp
@@ -0,0 +1,89 @@
+//
+// $Id: $
+//
+// Narya library - tools for developing networked games
+// Copyright (C) 2002-2007 Three Rings Design, Inc., All Rights Reserved
+// http://www.threerings.net/code/narya/
+//
+// This library is free software; you can redistribute it and/or modify it
+// under the terms of the GNU Lesser General Public License as published
+// by the Free Software Foundation; either version 2.1 of the License, or
+// (at your option) any later version.
+//
+// This library 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
+// Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public
+// License along with this library; if not, write to the Free Software
+// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+
+package com.threerings.util.env {
+
+import flash.utils.describeType;
+
+import com.threerings.util.ClassUtil;
+
+/**
+ * Flash Player specific implementation of Environment.
+ */
+public class Environment
+{
+    /**
+     * Return an array containing all the public field names of the object
+     */
+    public static function enumerateFields (obj :Object) :Array
+    {
+        var result :Array = [ ];
+        for each (var bit :String in describeType(obj)..variable.@name) {
+            result.push(bit);
+        }
+        return result;
+    }
+
+    /**
+     * Returns true if an object of type srcClass is a subclass of or
+     * implements the interface represented by the asClass paramter.
+     *
+     * <code>
+     * if (ClassUtil.isAssignableAs(Streamable, someClass)) {
+     *     var s :Streamable = (new someClass() as Streamable);
+     * </code>
+     */
+    public static function isAssignableAs (
+            asClass :Class, srcClass :Class) :Boolean
+    {
+        if (asClass == srcClass) {
+            return true;
+
+        // if not the same class and srcClass is Object, we're done
+        } else if (srcClass == Object) {
+            return false;
+        }
+
+        // ok, let's introspect on the class and see what we've got.
+        var typeInfo :XMLList = describeType(srcClass).child("factory");
+
+        // See which classes we extend.
+        var exts :XMLList = typeInfo.child("extendsClass").attribute("type");
+        var type :String;
+        for each (type in exts) {
+            if (asClass == ClassUtil.getClassByName(type)) {
+                return true;
+            }
+        }
+
+        // See which interfaces we implement.
+        var imps :XMLList = typeInfo.child("implementsInterface")
+            .attribute("type");
+        for each (type in imps) {
+            if (asClass == ClassUtil.getClassByName(type)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+}
+}
diff --git a/src/as/com/threerings/util/env/Environment.as-tm b/src/as/com/threerings/util/env/Environment.as-tm
new file mode 100644
index 000000000..e0bf5236b
--- /dev/null
+++ b/src/as/com/threerings/util/env/Environment.as-tm
@@ -0,0 +1,60 @@
+//
+// $Id: $
+//
+// Narya library - tools for developing networked games
+// Copyright (C) 2002-2007 Three Rings Design, Inc., All Rights Reserved
+// http://www.threerings.net/code/narya/
+//
+// This library is free software; you can redistribute it and/or modify it
+// under the terms of the GNU Lesser General Public License as published
+// by the Free Software Foundation; either version 2.1 of the License, or
+// (at your option) any later version.
+//
+// This library 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
+// Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public
+// License along with this library; if not, write to the Free Software
+// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+
+package com.threerings.util.env {
+
+import flash.utils.getQualifiedClassName;
+import flash.utils.getDefinitionByName;
+import avmplus.*;
+
+/**
+ * Tamarin specific implementation of Environment.
+ */
+public class Environment
+{
+    /**
+     * Return an array containing all the public field names of the object
+     */
+    public static function enumerateFields (obj :Object) :Array
+    {
+        if (obj != null) {
+            return Domain.currentDomain.getVariables(obj);
+        }
+    }
+
+    /**
+     * Returns true if an object of type srcClass is a subclass of or
+     * implements the interface represented by the asClass paramter.
+     *
+     * <code>
+     * if (ClassUtil.isAssignableAs(Streamable, someClass)) {
+     *     var s :Streamable = (new someClass() as Streamable);
+     * </code>
+     */
+    public static function isAssignableAs (asClass :Class, srcClass :Class) :Boolean
+    {
+        if (asClass != null && srcClass != null) {
+            return Domain.currentDomain.isAssignableAs(asClass, srcClass);
+        }
+        return false;
+    }
+}
+}