I too was confused by the use of the word "opaque".
It's a standard term in data structures, for a thing which A hands to B,
and B can only use to hand back to A, not peek inside it.
So I guess it's closest to this:
3.a) So obscure as to be unintelligible
Not wanting to beat a dead horse - if this has already been flogged,
please forgive me.
You're forgiven. If you ever come up to Cambridge, we can arrange in
person forgiveness, preferably with beer.
R's,
John
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