dbfo keep-together for informal objects?

Hi,

I want to make sure that some special <para>s are kept together on one page 
for print output.

I've seen that the dbfo keep-together PI is used for that. It works well if 
you put a formal object like <example> around the paras. But because I just 
want to group those paras and not add a title and an example number in front 
of it I can not use it.

It seems like keep-together is just supported for formal objects, not for 
informal ones. Is there any reason behind this?

How can I keep my paras together without using hacks like hard page breaks?

Kind regards,

Gerd