Excelsior is seemingly different things to different people depending
where you are in the world.
Judy Vorfeld mentioned that the envelope A-2 is approx. 5 3/4" x 4 1/4"
I must confess I have not previously come across an A-Series
envelopes. On this side of the pond we use C Series and to a lesser
extent B Series for envelopes and the A Series for the paper in which
A2 represents 420mm x 594mm (approx. 16 1/2" x 23 3/8").