Returns a type specifier for the characters handled by a specified external format.
external-format
external-format-type external-format => type-specifier
An external character format.
type-specifier
A type specifier describing the character types handled by external-format .
Takes the name of an external format, and returns a type specifier for the type of characters that the external format handles on the Lisp side.
external-format-foreign-type