search-unencodable-char
search-unencodable-char is an interactive compiled Lisp function in `mule-cmds.el
'.
(search-unencodable-char CODING-SYSTEM)
Search forward from point for a character that is not encodable.
It asks which coding system to check.
If such a character is found, set point after that character.
Otherwise, don't move point.
When called from a program, the value is the position of the unencodable
character found, or nil if all characters are encodable.