The Popup class provides functionality for displaying an absolutely
positioned element at a particular location in the window. It's designed to
be used as the foundation for building controls like a menu or tooltip. The
Popup class includes functionality for displaying a Popup near adjacent to
an anchor element.
This works cross browser and thus does not use IE's createPopup feature
which supports extending outside the edge of the brower window.
Encapsulates a popup position where the popup absolutely positioned by
setting the left/top style elements directly to the specified values.
The position is generally relative to the element's offsetParent. Normally,
this is the document body, but can be another element if the popup element
is scoped by an element with relative position.
Encapsulates a popup position where the popup is anchored at a corner of
an element.
When using AnchoredPosition, it is recommended that the popup element
specified in the Popup constructor or Popup.setElement be absolutely
positioned.
Encapsulates a popup position where the popup is positioned relative to the
window (client) coordinates. This calculates the correct position to
use even if the element is relatively positioned to some other element. This
is for trying to position an element at the spot of the mouse cursor in
a MOUSEMOVE event. Just use the event.clientX and event.clientY as the
parameters.