U+10000..U+3FFFF F0 90..BF 80..BF 80..BF
U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF
U+100000..U+10FFFF F4 80..8F 80..BF 80..BF
Note the A0..BF in U+0800..U+0FFF, the 80..9F in U+D000...U+D7FF,
the 90..BF in U+10000..U+3FFFF, and the 80...8F in U+100000..U+10FFFF.
U+10000..U+3FFFF F0 90..BF 80..BF 80..BF
U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF
U+100000..U+10FFFF F4 80..8F 80..BF 80..BF
Note the A0..BF in U+0800..U+0FFF, the 80..9F in U+D000...U+D7FF,
the 90..BF in U+10000..U+3FFFF, and the 80...8F in U+100000..U+10FFFF.