141. Any modifier of an impersonal verb (50) or of a verb used
impersonally, that is, with an infinitive or clause for its subject,
or without any definitely expressed or personal subject (as in "it is
cold," "it seems too early"), must necessarily be adverbial:
Estas varme en la domo, it is warm in the house.
Estos malvarme morgaux, it will be cold tomorrow.
Estas bone ke li venis, it is well that he came.
Estas amuze ke ni forgesis lin, it is amusing that we forgot him.
Ke vi venis estis tre sagxe, that you came was very wise.
Estos pli agrable en la salono, it will be pleasanter in the parlor.