  plmtex(side, disp, pos, just, text)
  ***********************************

  plmtex

  Writes text at a specified position relative to the viewport boundaries.
  Text may be written inside or outside the viewport, but is clipped at the
  subpage boundaries. The reference point of a string lies along a line
  passing through the string at half the height of a capital letter. The
  position of the reference point along this line is determined by just, and
  the position of the reference point relative to the viewport is set by disp
  and pos.

  side (char *, input): Specifies the side of the viewport along which the
  text is to be written. The string must be one of:

   o b: Bottom of viewport.
   o l: Left of viewport, text written parallel to edge.
   o lv: Left of viewport, text written at right angles to edge.
   o r: Right of viewport, text written parallel to edge.
   o rv: Right of viewport, text written at right angles to edge.
   o t: Top of viewport.

  disp (PLFLT, input): Position of the reference point of string, measured
  outwards from the specified viewport edge in units of the current character
  height. Use negative disp to write within the viewport.

  pos (PLFLT, input): Position of the reference point of string along the
  specified edge, expressed as a fraction of the length of the edge.

  just (PLFLT, input): Specifies the position of the string relative to
  its reference point. If just=0, the reference point is at the left and if
  just=1, it is at the right of the string. Other values of just give
  intermediate justifications.

  text (char *, input): The string to be written out.

