Object.InternalSlot
type t('M, 'T) = ('M, t'('M, 'T));
and t'('M, 'T) = {
id: Identifier.t('M, 'M),
value: Type.t('M, 'T),
optional: bool,
static: bool,
_method: bool,
comments: option(Syntax.t('M, unit)),
};