Although it is often debated, some typesetting rules say there should be different amounts of space after various punctuation marks. For example, the Chicago typesetting manual says that a period at the end of a sentence should have twice as much space following it as would a comma or a period as part of an abbreviation.
gtroff does this by flagging certain characters (normally
‘!’, ‘?’, and ‘.’) as end-of-sentence characters.
gtroff encounters one of these characters at the end of a
line, it appends a normal space followed by a sentence space in
the formatted output. (This justifies one of the conventions mentioned
in Input Conventions.)
In addition, the following characters and symbols are treated
transparently while handling end-of-sentence characters: ‘"’,
‘'’, ‘)’, ‘]’, ‘*’,
cflags request in Using Symbols, for more details.
To prevent the insertion of extra space after an end-of-sentence
character (at the end of a line), append