  The increasing complexity of software systems and the influence of
software-supported decisions in our society have sparked the need for software
that is safe, reliable, and fair. Explainability has been identified as a means
to achieve these qualities. It is recognized as an emerging non-functional
requirement (NFR) that has a significant impact on system quality. However, in
order to develop explainable systems, we need to understand when a system
satisfies this NFR. To this end, appropriate evaluation methods are required.
However, the field is crowded with evaluation methods, and there is no
consensus on which are the "right" ones. Much less, there is not even agreement
on which criteria should be evaluated. In this vision paper, we will provide a
multidisciplinary motivation for three such quality criteria concerning the
information that systems should provide: comprehensibility, fidelity, and
assessability. Our aim is to to fuel the discussion regarding these criteria,
such that adequate evaluation methods for them will be conceived.
