getImplicitRole = (type, attributes) => {
  let implicitRole;
  if (implicitRoles[type]) {
    implicitRole = implicitRoles[type](attributes);
  }
  if (roles.has(implicitRole)) {
    return implicitRole;
  }
  return null;
}
Returns an element's implicit role given its attributes and type.
Some elements only have an implicit role when certain props are defined.