onDragIn

fires when the item is dragged over some target the item can be dropped to

boolean onDragIn(string|number sId,string|number tId,object sObject,object tObject);

sId	string\|number	id of the dragged item
tId	string\|number	id of the potential drop landing
sObject	object	dhtmlXTreeObject instance of the source tree
tObject	object	dhtmlXTreeObject instance of the target tree

boolean

true to allow dropping

myTree.attachEvent("onDragIn", function(sId, tId, sObject, tObject){
    // your code here
});