pic: solid vs filled shapes

[Dave Kemper]

Hi all, I'm trying to understand some basic pic behavior.

I'm starting with this input; let's call it "picfile":

    .PS
    box;
    .PE

Then "groff -p picfile" produces a simple unfilled rectangle (that is, just the 
outline).

According to section 6.9 of "Making Pictures With GNU PIC" (doc/pic.ms), there 
are two ways to turn this into a filled box: put a "fill 1" or a "solid" after 
the "box".  The first of these works, producing a solid black rectangle:

    $ sed 's/box/box fill 1/' picfile | groff -p

But the second does not; it produces the same output as the unadorned "box":

    $ diff <(sed 's/box/box solid/' picfile | pic) <(cat picfile | pic) | wc
          0       0       0

I know that pic recognizes the word "solid," because changing it to something 
else produces a syntax error:

    $ sed 's/box/box stolid/' picfile | pic > /dev/null
    pic:<standard input>:2: there is no variable 'stolid'
    pic:<standard input>:2: giving up on this picture

But the "solid" modifier has no effect on the drawn box.

Am I doing something wrong?  Is pic?