\starttext
\dorecurse{4}{\page[empty]}% Every page will say "Page 1"
\stoptext
</texcode>
\setlayer[pagenumber]{Page \pagenumber}
\stopsetups
\setupbackgrounds[page][setups=layer,background=pagenumber]
\starttext
\dorecurse{4}{\page[empty]} % You get "Page 1, Page 2" etc.
\stoptext
</texcode>
Another solution was given by Wolfgang on the mailing list on February 21, 2012. He writes: ''Here is a slightly different version which is better when you need more dynamic layers.''
<texcode>
\definelayer [pagenumber][width=\overlaywidth,height=\overlayheight,preset=middle]
\defineoverlay[pagenumber][\texsetup{layer}]
\startsetups layer
\setlayer[pagenumber]{Page \pagenumber}
\tightlayer[pagenumber]
\stopsetups
\dorecurse{4}{\page[empty]}
\stoptext
</texcode>