F.2. Specification

The FSS-UTF encodes character values in the range [0, 0x7FFFFFFF]6 using multi-byte characters of lengths 1, 2, 3, 4, 5, and 6 bytes. For all encodings of more than one byte, the initial byte determines the number of bytes used by setting 1 in the equivalent number of high-order bytes. The next most significant bit is always 0. For example, a 2-byte sequence starts with 110 and a 6-byte sequence starts with 1111110.

The following table shows the format of the first byte of a character; the free bits available for coding the character are indicated by an x.

Byte	Value	Bits Free
First of 2 bytes	110xxxxx	5
First of 3 bytes	1110xxxx	4
First of 4 bytes	11110xxx	3
First of 5 bytes	111110xx	2
First of 6 bytes	1111110x	1
All subsequent bytes	10xxxxxx	6

Therefore, any byte that does not start with 10 is the start of an FSS-UTF character sequence. The table below illustrates the FSS-UTF:

Bits	Hex Min	Hex Max	Byte Sequence in Binary
7	00000000	0000007f	0vvvvvvv
11	00000080	000007FF	110vvvvv 10vvvvvv
16	00000800	0000FFFF	1110vvvv 10vvvvvv 10vvvvvv
21	00010000	001FFFFF	11110vvv 10vvvvvv 10vvvvvv 10vvvvvv
26	00200000	03FFFFFF	111110vv 10vvvvvv 10vvvvvv 10vvvvvv 10vvvvvv
31	04000000	7FFFFFFF	1111110v 10vvvvvv 10vvvvvv 10vvvvvv 10vvvvvv 10vvvvvv

The Unicode value is just the concatenation of the v bits in the multibyte encoding. When there are multiple ways to encode a value, for example U+0000, only the shortest encoding is legal.