An important concept in
gtroff is the break. When a break
gtroff outputs the partially filled line (unjustified),
and resumes collecting and filling text on the next output line.
There are several ways to cause a break in
gtroff. A blank line
not only causes a break, but it also outputs a one-line vertical space
(effectively a blank line). Note that this behaviour can be modified
with the blank line macro request
blm. See Blank Line Traps.
A line that begins with a space causes a break and the space is output
at the beginning of the next line. Note that this space isn't adjusted,
even in fill mode; however, the behaviour can be modified with the
leading spaces macro request
lsm. See Leading Spaces Traps.
The end of file also causes a break – otherwise the last line of the document may vanish!
Certain requests also cause breaks, implicitly or explicitly. This is discussed in Manipulating Filling and Adjusting.