Just stumbled on this -- if it's any use, here is an expanded version of these ideas, from the paper I gave at last years' Moodle Moot April 2014, together with a full HowTo guide.
http://www.slideshare.net/PhineasdeThornleyHea/phin-head-long25mmarkingmodesinmoodlefinalfinal
specifically, see Footnote 3, page 35
Phin Head
dBs Music