title: Events bubbling in dart
body: <p>I have a layer full of pictures (children), when mouse is over layer i'd like to know mouse coordinates with respect to the parent layer and one of the pictures.
  I am failing to do so. To demonstrate the problem I came up with a simple example:
  1 layer with one child picture and trigger on-mouse-over event.</p>
  
  <p>Consider the following:</p>
  
  
  
  <pre class="lang-html prettyprint-override"><code>&lt;!DOCTYPE html&gt;
  &lt;html&gt;
  &lt;head&gt;   
    &lt;title&gt;bubbles&lt;/title&gt;   
  &lt;/head&gt;
  &lt;body&gt;
  &lt;div id="layer" style="width:1000px; height: 500px; border: 2px solid #8AC007;"&gt;
    &lt;img id="image" src="https://www.dartlang.org/logos/dart-logo.png" style="position:absolute; left: 100px; top:100px; width:100px; height:100px; border: 2px solid #8AC007;"&gt;   
  &lt;/div&gt;
  
  &lt;script type="application/dart" src="main.dart"&gt;&lt;/script&gt;
  &lt;script data-pub-inline src="packages/browser/dart.js"&gt;&lt;/script&gt;
  &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>and dart script:</p>
  
  
  
  <pre class="lang-dart prettyprint-override"><code>import 'dart:html';
  
  void main() {
    querySelector("#layer").onMouseMove.listen((e)=&gt;print("${e.target}: ${e.offset}"));
  }
  </code></pre>
  
  <p>When I move mouse over the layer (not image!) I get messages: <code>div: Point(x,y)</code>, where point (<code>e.offset</code>) is given in the coordinates of the layer; when I move mouse over the image I get messages: <code>img: Point(x, y)</code> with <code>e.offset</code> given in coordinates of the image. Bou NO listener was set for image.onMouseMove.</p>
  
  <p>Thus the questions:</p>
  
  <ol>
  <li>What is happening? Why does image.onMouseOver event get trigerred?</li>
  <li>Let's assume the answer to the previous question is that because image is an offspring of the layer. But what happens then with the event bubbling? Why does not event image.onMouseOver bubble higher in the DOM to the layer and trigger layer.onMouseOver event?</li>
  </ol>