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— ID: Q-specials revised: 2014-06-10 — # `\special` commands
TeX provides the means to express things that device drivers can do, but about which TeX itself knows nothing. For example, TeX itself knows nothing about how to include PostScript figures into documents, or how to set the color of printed text; but some device drivers do.
Instructions for such things are introduced to your document by means of `\special` commands; all that TeX does with these commands is to expand their arguments and then pass the command to the DVI file. In most cases, there are macro packages provided (often with the driver) that provide a human-friendly interface to the `\special`; for example, there's little point including a figure if you leave no gap for it in your text, and changing color proves to be a particularly fraught operation that requires real wizardry. LaTeX 2e has standard graphics and color packages that make figure inclusion, rotation and scaling, and color typesetting relatively straightforward, despite the rather daunting `\special` commands involved. (ConTeXt provides similar support, though not by way of packages.)
The allowable arguments of `\special` depend on the device driver you're using. Apart from the examples above, there are `\special` commands in the emTeX drivers (e.g., `dvihplj`, `dviscr`, etc.) that will draw lines at arbitrary orientations, and commands in `dvitoln03` that permit the page to be set in landscape orientation.
Note that `\special` behaves rather differently in pdfTeX, since there is no device driver around. There _is_ a concept of PDF specials, but in most cases `\special` will provoke a warning when used in pdfTeX.