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groff: Line Control

 
 5.14 Line Control
 =================
 
 It is important to understand how 'gtroff' handles input and output
 lines.
 
    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.
 
 produces
 
      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 '\$1') 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.
 
  -- Escape: \<RET>
  -- Escape: \c
  -- Register: \n[.int]
      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
      before '\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.
 
         * If no-fill mode is active (using the 'nf' request), the next
           input text line after '\c' is handled as a continuation of the
           same input text line.
 
                .nf
                This is a \c
                test.
                    => This is a test.
 
         * If fill mode is active (using the 'fi' request), a word
           interrupted with '\c' is 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 than '\c', flushing out the current partial line in the
      usual way.
 
      The '.int' register contains a positive value if the last output
      line was interrupted with '\c'; this is associated with the current
      environment (Environments).
 

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