A bit of a follow-up to this.
I have found that the only way dragDropHandler and dragOverHandler respond is if the DragSource object's format is "treeDataGridItems".
I had been using a custom format name.
Frankly this seems limiting and I think the use of quoted strings versus references to static constants is something that should be reconsidered.
Each control expects a certain default DragSource format. For ADG it is
treeDataGridItems. If you don't have that in the DragSource ADG's default
handling will not respond. You can override the ADG handling and accept
other formats if you wish.
Many of the protected drag handlers in AdvancedDataGrid reference private methods and properties, so I am not clear on how I would override the default "treeDataGridItems" through inheritance.
Were you implying I should just copy and paste the AdvancedDataGrid source into a new class and make the appropriate substitutions?
Sorry, you don't override through inheritance, you assign listeners to the
events and call preventDefault() to stop the default behavior.