What’s a plate form?
Joy's use of basic etymology.
plat•form (plătˈfôrmˌ)
1540s, "plan of action, scheme, design," from Middle French plateforme, platte fourme, literally "flat form," from Old French plat "flat" (see plateau (n.)) + forme "form" (see form (n.)).
Political meaning, "statement of party policies," is from 1803, probably originally an image of a literal platform on which politicians gather, stand, and make their appeals, and perhaps influenced by earlier sense of "set of rules governing church doctrine" (first attested 1570s)--http://www.etymonline.com