.ev

.ev [n]

Change environment to n. For example, many requests that affect horizontal position, hyphenation, or text adjustment are stored in the current environment. If n is omitted, restore previous environment. The initial value of n is 0, and 0 n 2. You must return to the previous environment by using .ev with no argument, or you will get a stack overflow. (ditroff simply ignores an invalid argument and issues a warning.)