[XeTeX] \centerline on custom paper size with plain XeTeX

[Deepak Jois]

I want \centerline to properly center a line on a page with a custom
size. The minimal example below does not work for me. I even tried to
compile the code with "xetex -papersize=a5" What am I missing?

Code:

\special{papersize=5.8in,8.3in}
\hoffset0in
\hsize5.8in
\centerline{hi there}
\bye