Add 'role' data attribute. Note, that 'role' attribute is a part of reach ARIA API described here: http://www.w3.org/TR/wai-aria/ Among 'role', it defines lots of aria-* attributes

type r = {A : int, B : int, C : float}
type string = int

val x : r = {A = 1, B = "hi", C = 2.3}