Hans,

many thanks for your reply Pablo.

I’m afraid that dimensions seem not to be adapted:

\definepapersize[main] [A4] [A4]
\definepapersize[extra][A4,landscape][A4,landscape]

\definelayer[test][x=.5\paperwidth, y=.5\paperheight,state=repeat]
\setlayer[test]{abcde}

\setupbackgrounds[page][background={test}]