Definitions

Byte

For the purposes of this document, byte means the same thing as Rust's u8 (corresponding to a natural number in the range 0 to 255 inclusive).

Character

For the purposes of this document, character means the same thing as Rust's char. That means, in particular:

there's exactly one character for each Unicode scalar value
the things that Unicode calls "noncharacters" are characters
there are no characters corresponding to surrogate code points

Sequence

When this document refers to a sequence of items, it means a finite, but possibly empty, ordered list of those items.

"character sequence" and "sequence of characters" are different ways of saying the same thing.

Prefix of a sequence

When this document talks about a prefix of a sequence, it means "prefix" in the way that abc is a prefix of abcde. The prefix may be empty, or the entire sequence.

NFC normalisation