[XeTeX] XeTeX equivalent to \pdfpagewidth ?

[Philip TAYLOR (Webmaster, Ret'd)]

I now see that the necessary primitives are referenced
on p.~54; it was clearly unfortunate that I searched for
"page width" and not for the corresponding PdfTeX
primitive in the first place !

Philip Taylor (Webmaster, Ret'd) wrote:
> 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 ?
>
> Philip Taylor