Counting code units using either CODEUNITS16 or CODEUNITS32 gives the same answer, unless supplementary characters or a surrogate pair is involved.
A Unicode supplementary character is specified using a surrogate pair.
這些字元包括大多數的控制字元和Unicode代理對(surrogate pair)中的單個字元。
The second character surrogate pair is not in the input buffer to be written.
