> <\body> The way documents is influenced by so called . The uses a so called (or context) to store both environment variables and . The environment variables are subdivided into two categories: built-in variables and additional variables provided by style files. Built-in variables usually affect the layout, while additional variables mostly serve computational purposes. In the next sections of this chapter, we will describe all built-in environment variables. A typical built-in environment variable is . The value of an environment variable may be permanently using and temporarily using the primitive: <\tm-fragment> Some text. <\tm-fragment> text.> Counters are typical environment variables defined in style-sheets. <\tm-fragment> <\enumerate> A weirdly numbered list... <\tm-fragment> A weirdly numbered list... > The typesetting language uses of variables. That means that macros can access and modify variables in their calling context. In the previous example, the macro locally initializes to (uses ) and the macro increments it by one and shows its value. Since locally redefines , the original value of is restored on exit. Each document comes with an with the initial values of environment values, their values just before we typeset the document. If an environment variable does not occur in the initial environment, then its initial value defaults to its value after typesetting the document style and possible additional packages. The initial environment before typesetting the style files and packages is built-in into the editor. Some variables, like header and footer variables, must be set inside the document, their initial environment value is ignored. Generally, they should be set by header and sectioning markup. <\traverse> >