Class Roo.dd.DropTarget.*enter
The function a {link Roo.dd.DragSource} calls once to notify this drop target that the source is now over the
target. This default implementation adds the CSS class specified by overClass (if any) to the drop element
and returns the dropAllowed config value. This method should be overridden if drop validation is required.
IMPORTANT : it should set this.overClass and this.dropAllowed
Config Options - Has None
Public Properties - Has None
Public Methods - Has None