The type of characters that fit in the Basic Multilingual Plane.
bmp-char is the type of characters that fit in the Unicode Basic Multilingual Plane, that is all characters that fit in 16 bits.
The Basic Multilingual Plane (BMP) is the range of Unicode code points below
bmp-char can be written to a stream or passed to the FLI with external format :bmp without ever getting an error.
bmp-char was new in LispWorks 7.0. In LispWorks 6.1 and earlier versions simple-char has the most similar meaning.
bmp-char has no obvious equivalent in LispWorks 6.1 and earlier versions, where simple-char is the closest thing, but in most cases when you used simple-char it actually better to use cl:character (or leave it as simple-char, because it is now a synonym for cl:character).
LispWorks® User Guide and Reference Manual - 01 Dec 2021 19:30:41