@ Here is a suggestion as to how to do caesurae that wipe out the stave 
@ lines underneath them.


@ This first function arranges to "erase" a rectangular area. Actually, 
@ it's more like covering it with white paint. This means you can also use 
@ it to cover rectangles with other shades grey or black.

@ You can call this function anywhere in a stave for all sorts of uses,
@ not only the caesuara. I'll show another examples below. When you call
@ this, you must give it five numbers. The first two specify the position
@ of the rectangle, relative to the next note and the bottom of the stave.
@ The next two numbers give the width and height of the rectangle,
@ measured from the fixed position. They may be positive or negative. The 
@ fifth number specifies the colour of the paint, with 0 being black and 1 
@ being white. A number like 0.5 is a mid shade of gray.

@ You must call this function with "overdraw" rather than "draw" to 
@ ensure that it is called after everything else has been drawn. Otherwise 
@ other things (especially stave lines) may go on top of what it draws.
@ See the examples in the stave below.

draw erase
  /grey exch def
  /bh exch def /bw exch def moveto
  0 bh rlineto bw 0 rlineto 0 bh neg rlineto bw neg 0 rlineto
  grey setgray fill 0 setgray
enddraw

@ This function uses the erase function to clear a rectangle, and then 
@ draws two diagonal lines in the space. This function takes only four
@ numbers, the position and size of the rectangle. The width and height 
@ are expected to be positive, so the position is assumed to be the 
@ bottom lefthand corner. You can fiddle with the numbers to change 
@ the size of the lines and their thickness.

draw caesura
  /h exch def /w exch def /y exch def /x exch def
  x y w h 1 draw erase

  @ The first line starts 1 point in from the left. Increase the
  @ number to move it to the right. 
  x 1 add y moveto 
 
  @ The line ends up 3 points further to the right and 7 points up.
  @ Change these numbers to vary its length and slope. 
  3 7 rlineto
  
  @ The second line starts 4 points in from the left.
  x 4 add y moveto 

  @ It has the same length and slope as the first line. You should
  @ probably keep these values in step.  
  3 7 rlineto
  
  @ The 0.5 here specifies the thickness of the line. Make it bigger
  @ if you want a fatter line. 
  0.5 setlinewidth stroke 
enddraw

@ This macro sets up an easy way to call the custom caesuara. It should 
@ be called before the end of a bar. It positions the white rectangle 10 
@ points to the left, and 13 points above the bottom of the stave (so it
@ wipes out only the top line). The size of the rectangle is 7 points 
@ wide and 8 points high. An extra 2 points of space are inserted in the
@ bar. You may need to change this.

*define caes [space 2 overdraw -10 13 7 8 caesura]

@ The idea is that you fiddle with the numbers above until you get it 
@ looking how you want it. Then just use &caes whenever you need it, and 
@ they will all look the same.


@ OK, now we've defined all this stuff, let's use it...

[stave 1 treble 1]

@ These bars show various ways of "painting over" rectangles
R! [overdraw 0 0 8 8 1 erase] |
R! [overdraw 0 0 -8 -8 0.5 erase] |
rr [overdraw -6 6 16 4 0.75 erase] rr |

@ This bar shows a regular caesura and the custom one
aaa//a &caes |

R! |
[endstave]