\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. LaTeX2e 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.,
dviscr, etc.) that will draw lines at arbitrary orientations, and commands in
dvitoln03 that permit the page to be set in landscape orientation.
\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.
Source: “special` commands” <FAQ-specials>`