'Moved all documentation from old .dartdoc files.'

tools/dom/templates/html/dart2js/impl_MouseEvent.darttemplate

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of $LIBRARYNAME;
 
 $(ANNOTATIONS)class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
   factory $CLASSNAME(String type,
       {Window view, int detail: 0, int screenX: 0, int screenY: 0,
       int clientX: 0, int clientY: 0, int button: 0, bool canBubble: true,
       bool cancelable: true, bool ctrlKey: false, bool altKey: false,
       bool shiftKey: false, bool metaKey: false, EventTarget relatedTarget}) {
 
     if (view == null) {
       view = window;
     }
     var event = document.$dom_createEvent('MouseEvent');
     event.$dom_initMouseEvent(type, canBubble, cancelable, view, detail,
         screenX, screenY, clientX, clientY, ctrlKey, altKey, shiftKey, metaKey,
         button, relatedTarget);
     return event;
   }
 $!MEMBERS
 
+  // TODO(amouravski): Move this documentation out of thise template files and
+  // put it into docs.json. Remember to add @DomName here.
+  /**
+   * The X coordinate of the mouse pointer in target node coordinates.
+   *
+   * This value may vary between platforms if the target node moves
+   * after the event has fired or if the element has CSS transforms affecting
+   * it.
+   */
   int get offsetX {
   if (JS('bool', '!!#.offsetX', this)) {
       return JS('int', '#.offsetX', this);
     } else {
       // Firefox does not support offsetX.
       var target = this.target;
       if (!(target is Element)) {
         throw new UnsupportedError(
             'offsetX is only supported on elements');
       }
       return this.clientX - this.target.getBoundingClientRect().left;
     }
   }
 
+  /**
+   * The Y coordinate of the mouse pointer in target node coordinates.
+   *
+   * This value may vary between platforms if the target node moves
+   * after the event has fired or if the element has CSS transforms affecting
+   * it.
+   */
   int get offsetY {
     if (JS('bool', '!!#.offsetY', this)) {
       return JS('int', '#.offsetY', this);
     } else {
       // Firefox does not support offsetY.
       var target = this.target;
       if (!(target is Element)) {
         throw new UnsupportedError(
             'offsetY is only supported on elements');
       }
       return this.clientY - this.target.getBoundingClientRect().top;
     }
   }
 }