From S/Z, Barthes (p. 216-217):
Like the Marquise, the classic text is pensive: replete with meaning (as we have seen), it still seems to be keeping in reserve some ultimate meaning, one it does not express but whose place it keeps free and signifying: this zero degree of meaning (which is not its annulment, but on the contrary its recognition), this supplementary, unexpected meaning which is the theatrical sign of the implicit, is pensiveness: the pensive (in faces, in texts) is the signifier of the inexpressible, not of the unexpressed. For if the classic text has nothing more to say than what it says, at least it attempts to “let it be understood” that it does not say everything; this allusion is coded by pensiveness, which is a sign of nothing but itself: as though, having filled the text but obsessively fearing that it is not incontestably filled, the discourse insisted on supplementing it with an et cetera of plentitudes. Just as the pensiveness of a face signals that this head is heavy with unspoken language, so the (classic) text inscribes within its system of signs the signature of its plenitude: like the face, the text becomes expressive (let us say that it signifies its expressivity), endowed with an interiority whose supposed depth compensates for the parsimony of its plural. At its discreet urging, we want to ask the classic text: What are you thinking about? but the text, wilier than all those who try to escape by answering: about nothing, does not reply, giving meaning its last closure: suspension.