Mouse event bubbling might produce unexpected results

The unexpected consequences of the mouse event bubbling are best illustrated with an example. Consider the following HTML markup (and note that in real life you should not declare event handlers in HTML markup):

<div onmouseover="d_a()" onmouseout="d_b()">
  <p onmouseover="p_a()" onmouseout="p_b()">Line 1</p>
  <p>Line 2</p>
</div>

When the mouse is moved from outside the DIV to the first line, d_a and p_a are called as expected. When the mouse moves from Line 1 to Line 2, p_b (expected), as well as p_a (highly unexpected) are called even though the mouse has not left the DIV. p_a is called due to event bubbling; the mouseover event bubbles from its target through all the target's ancestors toward the document object.

Probably the best workaround is to compare the event target (browser-dependent, use xEvent to get browser-independent code) with the current element.