%
% Empty
%
> \boxXX=
\hbox(0.0+0.0)x0.0
%
% One
%
> \boxXX=
\hbox(0.5+0.5)x100.0
.\glue -1.0
.\rule(0.5+0.5)x103.0
.\glue -2.0
%
% Several, same width
%
> \boxXX=
\hbox(0.5+0.5)x300.0
.\glue -1.0
.\rule(0.5+0.5)x303.0
.\glue -2.0
%
% Mixed
%
> \boxXX=
\hbox(2.5+2.5)x300.0
.\glue -1.0
.\rule(0.5+0.5)x103.0
.\glue -2.0
.\glue -1.0
.\rule(1.5+1.5)x103.0
.\glue -2.0
.\glue -1.0
.\rule(2.5+2.5)x103.0
.\glue -2.0
%
% No rule at all
%
> \boxXX=
\hbox(1.0+1.0)x400.0
.\glue -1.0
.\rule(1.0+1.0)x103.0
.\glue -2.0
.\glue 200.0
.\glue -1.0
.\rule(1.0+1.0)x103.0
.\glue -2.0