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\doccite{Unicode Text Segmentation} [online].

Edited by Mark Davis. Revision 35; issued for Unicode 12.0.0. 2019-02-15 [viewed 2020-02-23].

Available from: \url{http://www.unicode.org/reports/tr29/tr29-35.html}

\doccite{Unicode Identifier and Pattern Syntax} [online].

Edited by Mark Davis. Revision 33; issued for Unicode 13.0.0.

2020-02-13 [viewed 2021-06-08].

\diffref{lex.name}

Previously valid identifiers containing characters

not in Normalization Form C, are now rejected.

Prevent confusing characters in identifiers.

Standard Ecma-262, third edition, 1999.

The Unicode Consortium.

Edited by Ken Whistler and Lauren\c{t}iu Iancu.

Available from: \url{http://www.unicode.org/reports/tr44/}

\indextext{name!length of}%

\indextext{name}%

The character classes XID_Start and XID_Continue

\begin{footnote}

On systems in which linkers cannot accept extended

characters, an encoding of the \grammarterm{universal-character-name} can be used in

}

\newcommand{\uname}[1]{\textsc{#1}}

\newcommand{\unicode}[2]{\ucode{#1} \uname{#2}}

\newcommand{\NTS}[1]{\textsc{#1}}

\newcommand{\ntbs}{\NTS{ntbs}}

\newcommand{\ntmbs}{\NTS{ntmbs}}

\rSec1[uaxid.general]{General}

This Annex describes the choices made in application of

how they do or do not apply to \Cpp{}.

\Cpp{} conforms by meeting the requirements

R1 ``Default Identifiers'' and

R4 ``Equivalent Normalized Identifiers''.

\rSec2[uaxid.def.general]{General}

The general syntax is

\begin{codeblock}

<Identifier> := <Start> <Continue>* (<Medial> <Continue>+)*

to the set of permitted \tcode{<Start>} characters,

the \tcode{<Medial>} set is empty, and

the \tcode{<Continue>} characters are unmodified.

\begin{codeblock}

<Identifier> := <Start> <Continue>*

<Start> := XID_Start + @\textrm{\ucode{005f}}@

\rSec2[uaxid.def.rfmt]{R1a Restricted format characters}

it must define a profile allowing them, or

describe precisely which combinations are permitted.

\rSec2[uaxid.def.stable]{R1b Stable identifiers}

that identifiers are stable across versions of the Unicode Standard.

Once a string qualifies as an identifier it does so in all future versions.

\Cpp{} does not make this guarantee,

the stability of the XID_Start and XID_Continue properties.

\rSec1[uaxid.immutable]{R2 Immutable identifiers}

\rSec1[uaxid.pattern]{R3 Pattern_White_Space and Pattern_Syntax characters}

such as computer languages should describe and implement

their use of whitespace and syntactically significant characters

during the processes of lexing and parsing.

\rSec1[uaxid.eqn]{R4 Equivalent normalized identifiers}

how identifiers are compared and considered equivalent.

If any characters are excluded from normalization,

\Cpp{} does not make any such exclusions.

implementations should estimate the width of a string

as the sum of estimated widths of

the first code points in its extended grapheme clusters.

The estimated width of the following code points is 2:

\begin{itemize}

\item \ucode{1100} -- \ucode{115f}

a UCS scalar value whose Unicode property \tcode{General_Category}

has a value in the groups \tcode{Separator} (\tcode{Z}) or \tcode{Other} (\tcode{C}) or to

a UCS scalar value which has the Unicode property \tcode{Grapheme_Extend=Yes},

\item

\placeholder{CE} is not a Unicode encoding and