Most documents need more functionality beyond filling, adjusting and
implicit line breaking. In order to gain further functionality,
gtroff allows commands to be embedded into the text, in two ways.
The first is a request that takes up an entire line, and does some large-scale operation (e.g. break lines, start new pages).
The other is an escape that can be usually embedded anywhere in the text; most requests can accept it even as an argument. Escapes generally do more minor operations like sub- and superscripts, print a symbol, etc.