@Section
   @Title { "@Background" }
   @Tag { background }
@Begin
@PP
background.sym @Index { @@Background symbol }
The @@Background symbol will print its left parameter in the
background of its right parameter.  That is, the result has
the size of the right parameter, but the left parameter will
be printed first in the same space, with its marks aligned with
the marks of the right parameter.
@End @Section