A `Source` is a monadic streaming function that produces values independently of the input value.
interface HasValue : Type -> TypegetValue : t -> JSIO StringgetValue : HasValue t => t -> JSIO Stringvalue : HasValue t => MSF JSIO (ElemRef t) StringvalueOf : HasValue t => ElemRef t -> MSF JSIO i StringmeterValue : MSF JSIO (ElemRef HTMLMeterElement) DoublemeterValueOf : ElemRef HTMLMeterElement -> MSF JSIO i DoubleprogressValue : MSF JSIO (ElemRef HTMLProgressElement) DoubleprogressValueOf : ElemRef HTMLProgressElement -> MSF JSIO i DoublegetChecked : HTMLInputElement -> JSIO Boolchecked : MSF JSIO (ElemRef HTMLInputElement) BoolcheckedAt : ElemRef HTMLInputElement -> MSF JSIO i BoolwindowLocation : MSF JSIO i LocationwindowHash : MSF JSIO i String