Single-byte and multibyte characters in the same string

For a multibyte code set, a string might be composed of both single-byte and multibyte characters.

To represent mixed strings, this publication combines the formats for multibyte and single-byte characters. The next example represents a string with four characters, where the first and fourth characters are single-byte characters, and the second and third characters are multibyte characters that consist of 2 bytes each:
aA1A2B1B2b