Objects of the IString class and the I0String class can contain a mixture of single-byte characters and double-byte characters. All member functions allow for the mixture. The searching functions will not match a single-byte character with the second or subsequent byte of a double-byte character. Functions that return substrings will never separate the bytes of a double-byte character.
Although the double-byte characters are supported, you must be careful not to alter the contents of a string in a way that would corrupt the data. For example, the statement:
IString[n]='x';
would be an error if the nth byte of the IString was part of a double-byte character.