Triggered by a NodeInterface's bubbled "expand" event.
function(parent, records, suppressEvent) {
        var me = this,
            insertIndex = me.indexOf(parent) + 1,
            toAdd = [];

        // Used by the TreeView to bracket recursive expand & collapse ops
        // and refresh the size. This is most effective when folder nodes are loaded,
        // and this method is able to recurse.
        if (!suppressEvent) {
            me.fireEvent('beforeexpand', parent, records, insertIndex);
        }

        me.handleNodeExpand(parent, records, toAdd);

        // The add event from this insertion is handled by TreeView.onAdd.
        // That implementation calls parent and then ensures the previous sibling's joining lines are correct.
        // The datachanged event is relayed by the TreeStore. Internally, that's not used.
        me.insert(insertIndex, toAdd);

        // Triggers the TreeView's onExpand method which calls refreshSize,
        // and fires its afteritemexpand event
        if (!suppressEvent) {
            me.fireEvent('expand', parent, records);
        }
    }