<\body> One major family of markup tags for presentations concerns the traversal of the document during a presentation. The keys and are used respectively for going back and forth in the presentation. The keys and are used to go to the start end of the presentation. When using the style or when enabling the ``presentation tool'' in the menu, a menu and additional icons will appear, which can also be used for the traversal of your presentation. The most basic traversal tag is called a ``switch'', and allows the user to show different pieces of text in successive and mutually exclusive manner. The entire presentation itself usually consists of a switch, where the pieces are the successive ``slides'' of the presentation. After selection of the style, this switch can be inserted using or . You may jump from one screen to another one using and . Inside a switch, new ``branches'' can be inserted after or before the currently visible branch using or . Besides the switch, you may use to insert paragraph-wide switches, and to insert inline switches (similarly to displayed and inline formulas). Another popular way to traverse is presentation is to progressively unroll content. This can be done by inserting an tag using . Using a ``hack'' this tag can be combined with the and tags: first create the list environment, but remove the first (automatically inserted) tag. Next insert the unroll tag. When pressing inside the unroll tag, new items are created; you still have to use for inserting new branches to the unroll structure (in particular, several items could be unrolled at once). A variant of unrolling is unfolding. This is basically an unroll tag with exactly two branches, but different variants are available in depending on the desired rendering. In particular, some of the renderings display a button which may be pushed in order to fold or unfold some content. The input-output fields inside computer algebra sessions are also foldable. Similarly, the tags in are switches with two branches, again with different kinds of rendering. When using in combination with an external plug-in, such as a computer algebra system, you will notice that all input-output fields in are foldable. In addition, you can create so called ``'' using the items in the submenu. This allows you to switch back and forth between a given input to the system and the corresponding output. All markup for the traversal of presentations may be nested in a natural way. In the menu, you may specify whether unrolled and folded structures should be folded back after traversal. <\initial> <\collection>