Object.Indexer
type t'('M, 'T) = {
id: option(Identifier.t('M, 'M)),
key: Type.t('M, 'T),
value: Type.t('M, 'T),
static: bool,
variance: option(Variance.t('M)),
comments: option(Syntax.t('M, unit)),
};
and t('M, 'T) = ('M, t'('M, 'T));