Text.PrettyPrint.HughesPJ inserting blank lines

I've found myself using "$+$ space $+$" in order to insert a blank line between two docs. There are probably other ways to do it. "(test "")" (and $$) instead of "space" (or $+$) also work in many cases (but not "empty"). Which way would be the best? Maybe one could add a further function "$++$" to do this and a list version "vsep" of "$++$"? Another idea might be something like a vertical space "vspace" so that several blank lines would be created by: $$ vspace $$ vspace $$ ... Cheers Christian