groff: Implicit Line Breaks
5.1.5 Implicit Line Breaks
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An important concept in 'gtroff' is the "break". When a break occurs,
'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'. ⇒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'. ⇒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.