After examining other threads, it seems that the
kh option has different purpose than I thought. However, I think that at least as a URL parameter, it doesn't make sense: if the user wishes to go to the HTTPS DDG site, he will just use the https: protocol scheme — there is no need for a parameter. In any case, I think that a parameter that does what I thought
kh did (controlling protocol scheme in the results) would be beneficial for the users.
Also, interface settings parameters don't seem to affect the non-Javascript DDG page (do any settings have effect there?).