\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 colour of printed text; but some device drivers do.

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 comprehensible 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 colour proves to be a particularly fraught operation that requires real wizardry. LaTeX2e has standard graphics and colour packages that make file inclusion, rotation, scaling and colour via \specials all easy.

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.