Definitions

Unicode

References to Unicode in this document refer to the Unicode standard, version 16.0.

References to the Unicode character database refer to version 16.0.0.

NFC normalisation

References to NFC-normalised strings are talking about Unicode's Normalization Form C, defined in Unicode Standard Annex #15.

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
• there is a character for each unassigned code point

Notation for characters

This document identifies characters in the following ways:

Printable ASCII characters other than space are represented by themselves using highlighting like a. For example \ represents character U+005C (REVERSE SOLIDUS).

ASCII control characters and space are represented as follows:

Other characters are identified by hexadecimal scalar value and name, for example U+FEFF (BYTE ORDER MARK).

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.