[XeTeX] XeTeX equivalent to \pdfpagewidth ?

[Philip Taylor (Webmaster, Ret'd)]

Dear Colleagues --

Studying

	http://xml.web.cern.ch/XML/lgc2/xetexmain.pdf

I can see no mention of "page width".  What is the XeTeX method
for setting the page width, analogous to PdfTeX's \pdfpagewidth,
please ?  (Of course, I will also want to set the page height !).

Philip Taylor