Again, this is a public method (even more so than parse_body_arguments) and should not have its signature changed.  If we have `get_{query,body}_argument` methods we should also have the plural variants.  I'm tempted to argue that since the need to care about this distinction is so rare we shouldn't even have RequestHandler methods for these at all (applications that care can go to `request.{query,body}_arguments` directly), but I know that if we had started with distinguished argument methods I'd fight against the merged versions even harder.