[uaxid.def.general]

# Annex E (informative) Conformance with UAX #31 [[uaxid]](./#uaxid)

## E.2 R1 Default identifiers [[uaxid.def]](uaxid.def#general)

### E.2.1 General [uaxid.def.general]

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/uax31.tex#L24)

UAX #31 specifies a default syntax for identifiers
based on properties from the Unicode Character Database, UAX #44[.](#1.sentence-1)

The general syntax is

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

```
 where <Start> has the XID_Start property,<Continue> has the XID_Continue property, and<Medial> is a list of characters permitted between continue characters[.](#1.sentence-2)

For C++ we add the character U+005f low line, or _,
to the set of permitted <Start> characters,
the <Medial> set is empty, and
the <Continue> characters are unmodified[.](#1.sentence-3)

In the grammar used in UAX #31, this is

```
<Identifier> := <Start> <Continue>*
<Start> := XID_Start + U+005f
<Continue> := <Start> + XID_Continue

```

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/uax31.tex#L45)

This is described in the C++ grammar in [[lex.name]](lex.name "5.11 Identifiers"),
where [*identifier*](lex.name#nt:identifier "5.11 Identifiers [lex.name]") is formed from[*identifier-start*](lex.name#nt:identifier-start "5.11 Identifiers [lex.name]") or[*identifier*](lex.name#nt:identifier "5.11 Identifiers [lex.name]") followed by [*identifier-continue*](lex.name#nt:identifier-continue "5.11 Identifiers [lex.name]")[.](#2.sentence-1)