code: def prefix(fonts, colours)
           text = StringIO.new
  
           text << "\\#{@justification.id2name}"
           text << "\\li#{@left_indent}"        unless @left_indent.nil?
           text << "\\ri#{@right_indent}"       unless @right_indent.nil?
           text << "\\fi#{@first_line_indent}"  unless @first_line_indent.nil?
           text << "\\sb#{@space_before}"       unless @space_before.nil?
           text << "\\sa#{@space_after}"        unless @space_after.nil?
           text << "\\sl#{@line_spacing}"       unless @line_spacing.nil?
           text << '\rtlpar' if @flow == RIGHT_TO_LEFT
  
           text.string.length > 0 ? text.string : nil
        end
docs: This method generates a string containing the prefix associated with a
   style object.
  
   ==== Parameters
   fonts::    A reference to a FontTable containing any fonts used by the
              style (may be nil if no fonts used).
   colours::  A reference to a ColourTable containing any colours used by
              the style (may be nil if no colours used).