* Optional. <p>A {@link Ext.DomQuery DomQuery} selector which identifies child elements within the Component's encapsulating
* Element which are the drag handles. This limits dragging to only begin when the matching elements are mousedowned.</p>
* <p>This may also be a specific child element within the Component's encapsulating element to use as the drag handle.</p>
* Optional. <p>A {@link Ext.DomQuery DomQuery} selector which identifies child elements within the Component's encapsulating
* Element which are the drag handles. This limits dragging to only begin when the matching elements are mousedowned.</p>
* <p>This may also be a specific child element within the Component's encapsulating element to use as the drag handle.</p>