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diff --git a/server/src/com/vaadin/event/dd/DropHandler.java b/server/src/com/vaadin/event/dd/DropHandler.java
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+/*
+ * Copyright 2011 Vaadin Ltd.
+ * 
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ * 
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+package com.vaadin.event.dd;
+
+import java.io.Serializable;
+
+import com.vaadin.event.Transferable;
+import com.vaadin.event.dd.acceptcriteria.AcceptAll;
+import com.vaadin.event.dd.acceptcriteria.AcceptCriterion;
+import com.vaadin.event.dd.acceptcriteria.ServerSideCriterion;
+
+/**
+ * DropHandlers contain the actual business logic for drag and drop operations.
+ * <p>
+ * The {@link #drop(DragAndDropEvent)} method is used to receive the transferred
+ * data and the {@link #getAcceptCriterion()} method contains the (possibly
+ * client side verifiable) criterion whether the dragged data will be handled at
+ * all.
+ * 
+ * @since 6.3
+ * 
+ */
+public interface DropHandler extends Serializable {
+
+    /**
+     * Drop method is called when the end user has finished the drag operation
+     * on a {@link DropTarget} and {@link DragAndDropEvent} has passed
+     * {@link AcceptCriterion} defined by {@link #getAcceptCriterion()} method.
+     * The actual business logic of drag and drop operation is implemented into
+     * this method.
+     * 
+     * @param event
+     *            the event related to this drop
+     */
+    public void drop(DragAndDropEvent event);
+
+    /**
+     * Returns the {@link AcceptCriterion} used to evaluate whether the
+     * {@link Transferable} will be handed over to
+     * {@link DropHandler#drop(DragAndDropEvent)} method. If client side can't
+     * verify the {@link AcceptCriterion}, the same criteria may be tested also
+     * prior to actual drop - during the drag operation.
+     * <p>
+     * Based on information from {@link AcceptCriterion} components may display
+     * some hints for the end user whether the drop will be accepted or not.
+     * <p>
+     * Vaadin contains a variety of criteria built in that can be composed to
+     * more complex criterion. If the build in criteria are not enough,
+     * developer can use a {@link ServerSideCriterion} or build own custom
+     * criterion with client side counterpart.
+     * <p>
+     * If developer wants to handle everything in the
+     * {@link #drop(DragAndDropEvent)} method, {@link AcceptAll} instance can be
+     * returned.
+     * 
+     * @return the {@link AcceptCriterion}
+     */
+    public AcceptCriterion getAcceptCriterion();
+
+}