--- a/graal/com.oracle.truffle.api/src/com/oracle/truffle/api/instrument/ASTInstrumentListener.java	Fri Apr 10 16:58:26 2015 -0700
+++ b/graal/com.oracle.truffle.api/src/com/oracle/truffle/api/instrument/ASTInstrumentListener.java	Fri Apr 10 17:55:09 2015 -0700
@@ -26,32 +26,50 @@
 
 import com.oracle.truffle.api.frame.*;
 import com.oracle.truffle.api.nodes.*;
+import com.oracle.truffle.api.source.*;
 
 /**
- * A listener of Truffle AST runtime execution events that can collect information, examine the
- * execution state at a particular node, and possibly intervene on behalf of an external tool.
+ * A receiver of Truffle execution events that can act on behalf of an external client.
+ * <p>
+ * The {@link Probe} argument provides access to the {@link SourceSection} associated with the
+ * event, as well as any {@link SyntaxTag}s that have been applied at that AST location.
+ * <p>
+ * This listener is designed for clients that also require access to the AST execution state at the
+ * time of the event. Clients that do not require access to the AST execution state should use the
+ * simpler {@link InstrumentListener}.
+ * <p>
+ * Clients are free, of course, to record additional information in the listener implementation that
+ * carries additional information about the context and reason for the particular {@link Instrument}
+ * that is to be created.
  */
 public interface ASTInstrumentListener {
 
     /**
      * Receive notification that an AST node's execute method is about to be called.
+     * <p>
+     * <strong>Synchronous</strong>: Truffle execution waits until the call returns.
      */
     void enter(Probe probe, Node node, VirtualFrame vFrame);
 
     /**
      * Receive notification that an AST Node's {@code void}-valued execute method has just returned.
+     * <p>
+     * <strong>Synchronous</strong>: Truffle execution waits until the call returns.
      */
     void returnVoid(Probe probe, Node node, VirtualFrame vFrame);
 
     /**
      * Receive notification that an AST Node's execute method has just returned a value (boxed if
      * primitive).
+     * <p>
+     * <strong>Synchronous</strong>: Truffle execution waits until the call returns.
      */
     void returnValue(Probe probe, Node node, VirtualFrame vFrame, Object result);
 
     /**
      * Receive notification that an AST Node's execute method has just thrown an exception.
+     * <p>
+     * <strong>Synchronous</strong>: Truffle execution waits until the call returns.
      */
     void returnExceptional(Probe probe, Node node, VirtualFrame vFrame, Exception exception);
-
 }

--- a/graal/com.oracle.truffle.api/src/com/oracle/truffle/api/instrument/InstrumentListener.java	Fri Apr 10 16:58:26 2015 -0700
+++ b/graal/com.oracle.truffle.api/src/com/oracle/truffle/api/instrument/InstrumentListener.java	Fri Apr 10 17:55:09 2015 -0700
@@ -24,31 +24,51 @@
  */
 package com.oracle.truffle.api.instrument;
 
+import com.oracle.truffle.api.source.*;
+
 /**
- * A listener of Truffle execution events that can collect information on behalf of an external
- * tool. Contextual information about the source of the event, if not stored in the implementation
- * of the listener, can be obtained via access to the {@link Probe} that generates the event.
+ * A receiver of Truffle execution events that can act on behalf of an external client.
+ * <p>
+ * The {@link Probe} instance provides access to the {@link SourceSection} associated with the
+ * event, as well as any {@link SyntaxTag}s that have been applied at that program's location.
+ * <p>
+ * This is the simplest kind of listener, suitable for clients that need no other information about
+ * the program's execution state at the time of the event. Clients that require access to the AST
+ * execution state should use {@link ASTInstrumentListener}.
+ * <p>
+ * Clients are free, of course, to record additional information in the listener implementation that
+ * carries additional information about the context and reason for the particular {@link Instrument}
+ * that is to be created from the listener.
  */
 public interface InstrumentListener {
 
     /**
-     * Receive notification that an AST node's execute method is about to be called.
+     * Receive notification that a program location is about to be executed.
+     * <p>
+     * <strong>Synchronous</strong>: Truffle execution waits until the call returns.
      */
     void enter(Probe probe);
 
     /**
-     * Receive notification that an AST Node's {@code void}-valued execute method has just returned.
+     * Receive notification that a program location's {@code void}-valued execution has just
+     * completed.
+     * <p>
+     * <strong>Synchronous</strong>: Truffle execution waits until the call returns.
      */
     void returnVoid(Probe probe);
 
     /**
-     * Receive notification that an AST Node's execute method has just returned a value (boxed if
-     * primitive).
+     * Receive notification that a program location's execution has just completed and returned a
+     * value (boxed if primitive).
+     * <p>
+     * <strong>Synchronous</strong>: Truffle execution waits until the call returns.
      */
     void returnValue(Probe probe, Object result);
 
     /**
-     * Receive notification that an AST Node's execute method has just thrown an exception.
+     * Receive notification that a program location's execution has just thrown an exception.
+     * <p>
+     * <strong>Synchronous</strong>: Truffle execution waits until the call returns.
      */
     void returnExceptional(Probe probe, Exception exception);
 }

--- a/graal/com.oracle.truffle.api/src/com/oracle/truffle/api/instrument/InstrumentationNode.java	Fri Apr 10 16:58:26 2015 -0700
+++ b/graal/com.oracle.truffle.api/src/com/oracle/truffle/api/instrument/InstrumentationNode.java	Fri Apr 10 17:55:09 2015 -0700
@@ -28,8 +28,9 @@
 import com.oracle.truffle.api.nodes.*;
 
 /**
- * A marker interface for Truffle {@linkplain Node nodes} that support <em>Instrumentation</em> and
- * are should not be part of any Guest Language execution semantics.
+ * A marker interface for Truffle {@linkplain Node nodes} that internally implement the
+ * <em>Instrumentation Framework</em>. Such nodes should not be part of any Guest Language execution
+ * semantics, and should in general not be visible to ordinary Instrumentation clients.
  */
 public interface InstrumentationNode {
 
@@ -39,7 +40,8 @@
     String instrumentationInfo();
 
     /**
-     * Events at a Truffle node that get propagated through the Instrumentation Framework.
+     * Events that propagate through the {@linkplain InstrumentationNode implementation nodes} of
+     * the Instrumentation Framework, not visible in this form to Instrumentation clients.
      */
     interface TruffleEvents {
 
@@ -62,6 +64,5 @@
          * An AST Node's execute method has just thrown an exception.
          */
         void returnExceptional(Node node, VirtualFrame vFrame, Exception exception);
-
     }
 }