15.4.2 Line Styles
Line styles are specified by the following properties:
     
- linestyle
- May be one of
          
- "-"
- Solid lines.
          
 
- "--"
- Dashed lines.
          
 
- ":"
- Points.
          
 
- "-."
- A dash-dot line. 
 
 
- linewidth
- A number specifying the width of the line.  The default is 1.  A value
of 2 is twice as wide as the default, etc.