<\body> provides a few other kinds of additional interfaces to external systems in addition to shell-like interfaces. First of all, it is possible to insert a so called ``executable switch'' anywhere in the document using . For instance, if is installed on your system, then should yield something like . You may enter a expression in the yellow part of this markup, say . Using , you may now switch back and forth between the unevaluated input and the evaluated output *+1|)>>>. Using , you enable multi-line input. This kind of executable switches are very useful for plug-ins such as >, , , , which are mainly used for the efficient computation and insertion of special graphics inside documents. Some plug-ins such as can even be selected as a using . When doing so, a special menu will appear, which allows for many useful operations directly on formulas. For instance, when putting the cursor inside the formula and pressing or , the formula gets evaluated automatically to yield . If a plug-in can be used as a scripting language, then it is possible to create executable switches with links between them. More precisely, assuming that you selected a scripting language from , you may insert a new using or . As before, when pressing , the current input is evaluated and you will see the corresponding output; you may switch back to the input by pressing once more. Contrary to executable switches, you may attach an identifier to the executable input field by disactivating the field or by editing the field in the focus bar. Inside other executable input fields, you may then refer to the value of the field by inserting a using or . As a variant to executable input fields, you may sometimes prefer to insert plain using or . These fields can only be used as inputs and pressing inside such a field will only recompute those other fields which depend on it. <\example> The excutable input fields may for instance be nice in pedagogic documents in which parts of the document may be modified and recomputed by the reader. For instance, evaluation of the input fragment <\quote-env> The derivative of >>> equals ,x)|*+1|)>>>>. The second derivative is given by ,x)|*+1|)>+x>>>. yields <\quote-env> The derivative of >>> equals ,x)|*+1|)>>>>. The second derivative is given by ,x)|*+1|)>+x>>>. Of course, if the reader changes the input function > into something else and presses , then the first and second derivatives will be updated automatically. <\initial> <\collection>