Some characters do not have a valid representation in Unicode.
These characters have some special values; they are made up of two Unicode characters in two specific ranges such that the first Unicode character is in one range (for example 0xD800-0xD8FF) and the second Unicode character is in the second range (for example 0xDC00-0xDCFF). This is called a surrogate pair.
If one of the Unicode characters are missing or if they are out of order, (only a partial character), it is an invalid name. Names of this type have been allowed in *TYPE1 directories, but are not allowed in *TYPE2 directories. In order for the conversion function to continue, the name is changed before the object is linked into the *TYPE2 directory if a name containing one of these invalid names is found.