It is important to understand how
gtroff handles input and output
Many escapes use positioning relative to the input line. For example, this
This is a \h'|1.2i'test. This is a \h'|1.2i'test.
This is a test. This is a test.
The main usage of this feature is to define macros that act exactly at the place where called.
.\" A simple macro to underline a word .de underline . nop \\$1\l'|0\[ul]' ..
In the above example, ‘|0’ specifies a negative distance from the
current position (at the end of the just emitted argument
back to the beginning of the input line. Thus, the ‘\l’ escape
draws a line from right to left.
gtroff makes a difference between input and output line
continuation; the latter is also called interrupting a line.
Continue a line.
\RET (this is a backslash at the end of a
line immediately followed by a newline) works on the input level,
suppressing the effects of the following newline in the input.
This is a \ .test ⇒ This is a .test
The ‘|’ operator is also affected.
\c works on the output level. Anything after this escape on the
same line is ignored except
\R, which works as usual. Anything
\c on the same line is appended to the current partial
output line. The next non-command line after an interrupted line counts
as a new input line.
The visual results depend on whether no-fill mode is active.
nfrequest), the next input text line after
\cis handled as a continuation of the same input text line.
.nf This is a \c test. ⇒ This is a test.
firequest), a word interrupted with
\cis continued with the text on the next input text line, without an intervening space.
This is a te\c st. ⇒ This is a test.
Note that an intervening control line that causes a break is stronger
\c, flushing out the current partial line in the usual way.
.int register contains a positive value if the last output
line was interrupted with
\c; this is associated with the current
environment (see Environments).