• dialog box is resizable
• WTL treeview doesn't store text strings for each tree item. Display of each item is done 'on demand', when TVN_GETDISPINFO notification message arrives
• tree items contain COM interface pointers as item data. In display phase these interfaces are queried to find out what text and bitmap to display for the DOM node or attribute in question
• tree is constructed dynamically. No child nodes are added until the node is expanded. Children nodes are deleted when parent is collapsed
• there is context menu that allows you to expand or collapse a node in its entirety, with all of its children, its children's children, and so on
• BHO and IE Extension objects may be loaded in different COM apartments. BHO registers its instances in Global Interface Table (GIT) so that Extension can call methods on it

The VC++ 6.0 project that comes with this article is an ATL in-process COM server, housing Browser Helper (BHO) and IE Extension objects. When the IE browser downloads HTML page, BHO will pop up a dialog box with a treeview which will display Document Object Model (DOM) nodes and attributes of that HTML document.