That's not correct. The Basic Multilingual Plane (like Unicode itself) is not an encoding, it is a subset of the Unicode codespace. UTF-8 restricted to sequence

That's not correct. The Basic Multilingual Plane (like Unicode itself) is not an encoding, it is a subset of the Unicode codespace. UTF-8 restricted to sequences of 3 bytes can only represent characters between U+0000 and U+FFFF inclusive, which happens to exactly contain the characters defined by the BMP.