Progressive inferential is a variant of focal inferential, denoting an action beginning some time before the time of reference,
and continuing presumably for some time after it,
and expresses that the knowledge of the fact is inferred from evidence,
be it sensorial perception, logical deduction or direct report from a trusted source.
That knowledge is most often presented as new information, sometimes unexpected, for the speaker himself.
The temporal distinction between a past and a present state, event or action is not marked grammatically,
the tense must be decided from the context.
It is used mostly in written language, and is typical of a factual or newspaper style.