Language Concepts (The GNU Troff Manual)

#### 6.1.1 Language Concepts

The fundamental operation of the GNU `troff` formatter is the translation of the `groff` input language into a device-independent form primarily concerned with what has to be written or drawn at specific positions on the output device. This language is simple and imperative. In the following discussion, the term command always refers to this intermediate output language, and never to the `groff` language intended for direct use by document authors. Intermediate output commands comprise several categories: glyph output; font, color, and text size selection; motion of the printing position; page advancement; drawing of geometric objects; and device control commands, a catch-all for operations not easily classified as any of the foregoing, such as directives to start and stop output, identify the intended output device, or place URL hyperlinks in supported output formats.