When you click OK in the Phones Class dialog box, the Undefined Characters in Class dialog box appears if the class contains characters that are not defined in the standard inventory.
In Phonology Assistant (PA), the phonetic characters consist primarily of the International Phonetic Alphabet (IPA) in the Unicode character encoding. PA includes several non-IPA characters in its standard inventory. Most are obsolete but are included for convenience and backward compatibility.
Do one of the following:
Leave the undefined characters in the class.
Modify the class to contain only characters defined in the standard inventory.