Notes on the Table of Contents

Just for reference, I'd like to make note of some of the other design options.

At a minimum, any tree navigator must include the immediate children of the current node. This doesn't provide any context, and relies on the browser's “back” command, so usually one would also include the immediate parent and the root, or perhaps the chain of parents leading back to the root.

The “vertical fixed” design used for this site can be turned into a “horizontal fixed” design by arranging the sets of siblings horizontally rather than vertically. The result is the design used by the file browser in the NeXT operating system—a nice design, but one that uses a lot of horizontal space.

The main disadvantage of these fixed designs relative to the nonfixed design used by a standard tree view is that it is not possible to expand multiple child nodes at the same time. The main advantage, of course, is that the upper layers remain fixed during navigation.

Independent of the options above, there is also the question of how to handle “wide nodes”, that is, nodes with many children. The horizontal fixed design handles these nodes gracefully, since the long list of children is confined to a single pane and does not interfere with navigation in the other panes. As noted in Exceptions to the Tree Structure, my ad hoc solution was to hide the child nodes and provide access through custom indices.

Speaking of a sense of stability, I noticed the following in What can we learn from Jakob Nielsen?.

this goes against the dicta of Macintosh Human Interface Guidelines; the genius of pull-down menus is stability of interface, an option that doesn't make sense in a particular context remains in the same place but greyed out—see the section of Chapter 4, The Menu Bar, where Apple says “Your application's menu titles should remain constant. This constancy adds to the user's sense of perceived stability of the interface and helps users identify applications when they switch from one to another.” The Macintosh way to do this would be to leave the “home” button but greyed out.