[pdftex] hiding optional content

[RS]

Hi,

I've been experimenting with optional content groups (OCGs), putting
them on top of each other with only one being visible at a time (which
one can be chosen by the user). Now, a PDF viewer that does not support
PDF 1.5 will display all layers at the same time. What I would like to
find is a way to make the optional content -- well... optional. Is there
any trick to hide the OCGs from older viewers?

Regards,
Robert.