groff: Filling and Adjusting
5.1.1 Filling and Adjusting
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When 'gtroff' reads text, it collects words from the input and fits as
many of them together on one output line as it can. This is known as
"filling".
Once 'gtroff' has a "filled" line, it tries to "adjust" it. This
means it widens the spacing between words until the text reaches the
right margin (in the default adjustment mode). Extra spaces between
words are preserved, but spaces at the end of lines are ignored. Spaces
at the front of a line cause a "break" (breaks are explained in ⇒
Implicit Line Breaks).
⇒Manipulating Filling and Adjusting.