Oh yeah, that's true -- I was just taking the viewpoint that the "surrogate range" as a block (as it relates to potential encoding errors) does not really need to be broken into the parts that map to the "supplemental private-use area", because this area is just part of the "higher planes" in the unicode space, and is addressed by surrogates in the same way as all the other planes above FFFF.

(Encode::Unicode implements unicode encodings like UTF-16)

Thanks for clarifying that -- this thread has been very educational for me.