%
% Same width
%
> \boxXX=
\hbox(1.0+1.0)x100.0
.\glue -1.0
.\rule(1.0+1.0)x103.0
.\glue -2.0
%
% Different borders
%
> \boxXX=
\hbox(1.0+1.0)x100.0
.\glue -3.0
.\rule(1.0+1.0)x107.0
.\glue -4.0
%
% Different widths
%
> \boxXX=
\hbox(2.0+2.0)x100.0
.\glue -1.0
.\rule(1.0+1.0)x103.0
.\glue -2.0
.\glue -100.0
.\glue -1.0
.\rule(2.0+2.0)x103.0
.\glue -2.0
%
% Different widths, second is 0pt
%
> \boxXX=
\hbox(1.0+1.0)x100.0
.\glue -1.0
.\rule(1.0+1.0)x103.0
.\glue -2.0