Based on the information contained in that part of "A" which is given, it will yield a specifc set of expectations for any proposed element of "A" (known or unknown). If the specific element happens to be a member of that part which is given the results will be 100% consistent with what was given. If the specific element is not a member of what is given it will either fit the expectations given or it will yield an alteration in the set of further expectations: i.e., it smoothly becomes a member of the given elements of "A".

As far as I am aware, that is exactly what an explanation does.

Have fun -- Dick