Stencils

[David Feuer]

ly:stencil-combine-at-edge says:
           "Construct a stencil by putting @var{second} next to @var{first}. "
           "@var{axis} can be 0 (x-axis) or 1 (y-axis), "
           "@var{direction} can be -1 (left or down) or 1 (right or up). "
           "The stencils are juxtaposed with  @var{padding} as extra space. "
           "If this puts the reference points closer than @var{minimum}, "
           "they are moved by the latter amount."
           "@var{first} and @var{second} may also be '() or #f.")

I'm a little confused.  What exactly happens when the reference points
are too close?  And why does this happen at the stencil level? 
Shouldn't all the decisions be made above that?  A few more things:

1.  Are stencils just created as an intermediate output format, or do
they participate in the process of adjusting the music to arrange all
the pieces as well as possible?

2.  The more I read the code and think about it, the more I think
stencil interpretation should be pushed to the back end and written in
Scheme.

3.  I really don't like stencil leaves being arbitrary scheme
expressions that produce output.  When the back end can't look inside
the box, it can't figure out the best way to deal with the contents.

David Feuer