load-label
to find and download labels for the given URL; any labels found
will be put on the statement list. We then run a pattern-matcher
over the now-modified statement list, looking for any label using
the rating service from "http://www.musac.org/"
and with an s rating less than 2. If the matcher finds no musac
label with an s dimension, it returns unknown,
and, if it finds such a label, it returns true or
false depending on whether or not the associated value
is less than 2.
The line false-if-unknown has the effect of
converting a returned value unknown to false;
this is a policy decision about which
semantics to give to three-valued logic, specifically about the
meaning of unknown. The overall effect is to allow viewing
of any document for which we can find at least a single label with a musac-s
rating less than 2.