File: groff.info,  Node: Line Layout,  Next: Line Continuation,  Prev: troff and nroff Modes,  Up: GNU troff Reference

5.15 Line Layout
================

The following drawing shows the dimensions that 'gtroff' uses for
placing a line of output onto the page.  They are labeled with the
request that manipulates each dimension.

          -->| in |<--
             |<-----------ll------------>|
        +----+----+----------------------+----+
        |    :    :                      :    |
        +----+----+----------------------+----+
     -->| po |<--
        |<--------paper width---------------->|

These dimensions are:

'po'
     "Page offset"--this is the leftmost position of text on the final
     output, defining the "left margin".

'in'
     "Indentation"--this is the distance from the left margin where text
     is printed.

'll'
     "Line length"--this is the distance from the left margin to right
     margin.

   The right margin is not explicitly configured; the combination of
page offset and line length provides the information necessary to derive
it.

   A simple demonstration:

     .ll 3i
     This is text without indentation.
     The line length has been set to 3\~inches.
     .in +.5i
     .ll -.5i
     Now the left and right margins are both increased.
     .in
     .ll
     Calling .in and .ll without parameters restores
     the previous values.

         => This  is text without indenta-
         => tion.   The  line  length  has
         => been set to 3 inches.
         =>      Now   the  left  and
         =>      right  margins   are
         =>      both increased.
         => Calling  .in  and  .ll without
         => parameters restores the previ-
         => ous values.

 -- Request: .po [offset]
 -- Request: .po +offset
 -- Request: .po -offset
 -- Register: \n[.o]
     Set page offset to OFFSET (or increment or decrement its current
     value by OFFSET).  If invoked without an argument, the page offset
     is restored to the value before the previous 'po' request.  This
     request does not cause a break; the page offset in effect when an
     output line is broken prevails (*note Manipulating Filling and
     Adjustment::).  The initial value is 1i and the default scaling
     unit is 'm'.  On terminal devices, the page offset is set to zero
     by a driver-specific macro file, 'tty.tmac'.  The current page
     offset can be found in the read-only register '.o'.  This request
     is incorrectly documented in the AT&T 'troff' manual as using a
     default scaling unit of 'v'.

          .po 3i
          \n[.o]
              => 720
          .po -1i
          \n[.o]
              => 480
          .po
          \n[.o]
              => 720

 -- Request: .in [indent]
 -- Request: .in +indent
 -- Request: .in -indent
 -- Register: \n[.i]
     Set indentation to INDENT (or increment or decrement the current
     value by INDENT).  This request causes a break.  Initially, there
     is no indentation.

     If 'in' is called without an argument, the indentation is reset to
     the previous value before the last call to 'in'.  The default
     scaling unit is 'm'.

     If a negative indentation value is specified (which is not
     allowed), 'gtroff' emits a warning in category 'range' and sets the
     indentation to zero.

     The effect of 'in' is delayed until a partially collected line (if
     it exists) is output.  A temporary indentation value is reset to
     zero also.

     The current indentation (as set by 'in') can be found in the
     read-only register '.i'.  The indentation is associated with the
     environment (*note Environments::).

 -- Request: .ti offset
 -- Request: .ti +offset
 -- Request: .ti -offset
 -- Register: \n[.in]
     Temporarily indent the next output line by OFFSET.  If an increment
     or decrement value is specified, adjust the temporary indentation
     relative to the value set by the 'in' request.

     This request causes a break; its value is associated with the
     environment (*note Environments::).  The default scaling unit is
     'm'.  A call of 'ti' without an argument is ignored.

     If the total indentation value is negative (which is not allowed),
     'gtroff' emits a warning in category 'range' and sets the temporary
     indentation to zero.  'Total indentation' is either OFFSET if
     specified as an absolute value, or the temporary plus normal
     indentation, if OFFSET is given as a relative value.

     The effect of 'ti' is delayed until a partially collected line (if
     it exists) is output.

     The read-only register '.in' is the indentation that applies to the
     current output line.

     The difference between '.i' and '.in' is that the latter takes into
     account whether a partially collected line still uses the old
     indentation value or a temporary indentation value is active.

 -- Request: .ll [length]
 -- Request: .ll +length
 -- Request: .ll -length
 -- Register: \n[.l]
 -- Register: \n[.ll]
     Set the line length to LENGTH (or increment or decrement the
     current value by LENGTH).  Initially, the line length is set to
     6.5i.  The effect of 'll' is delayed until a partially collected
     line (if it exists) is output.  The default scaling unit is 'm'.

     If 'll' is called without an argument, the line length is reset to
     the previous value before the last call to 'll'.  If a negative
     line length is specified (which is not allowed), 'gtroff' emits a
     warning in category 'range' and sets the line length to zero.  The
     line length is associated with the environment (*note
     Environments::).

     The current line length (as set by 'll') can be found in the
     read-only register '.l'.  The read-only register '.ll' is the line
     length that applies to the current output line.

     Similar to '.i' and '.in', the difference between '.l' and '.ll' is
     that the latter takes into account whether a partially collected
     line still uses the old line length value.