callback
A callback procedure invoked as treenode is about to be expanded. Expansion is done by double clicking on a node’s label, by single clicking on its expand symbol (a + sign), or by pressing the right arrow key when the node is selected. The + symbol changes to a - after expansion.
This callback is invoked only if the node was created with the "has dynamic children" setting. The callback should dynamically populate the node by calling treenode.add_child to add child nodes.
This procedure is a class procedure so can only be set via a treenode class name not via a treenode instance name, e.g. if a treenode "mynode" is of class "database_t", then database_t.populate can be set, but mynode.populate may not.
<treenode>.populate(<treenode>)