[XeTeX] centering layout with geometry package

[Daniel Greenhoe]

Using the geometry package, is there any way to automatically (without
using layouthoffset and layoutvoffset) to center a layout area on a
physical page? The default seems for the layout to be pushed into the
upper left corner of the physical page. Here is an example:

\documentclass{book}
\setlength{\parskip}{0mm}%
\setlength{\parindent}{0mm}%
\usepackage{geometry}
\geometry{
  xetex,truedimen,paper=a4paper,
  centering,twoside=false,
  ignoreall,
  layoutheight=200mm,layoutwidth=100mm,
  margin=10mm,
  nomarginpar,noheadfoot,
  showframe,showcrop
  }
\begin{document}%
abc
\end{document}%

Many thanks in advance,
Dan