[lex.header]

# 5 Lexical conventions [[lex]](./#lex)

## 5.6 Header names [lex.header]

[header-name:](#nt:header-name "5.6 Header names [lex.header]")  
< [*h-char-sequence*](#nt:h-char-sequence "5.6 Header names [lex.header]") >  
" [*q-char-sequence*](#nt:q-char-sequence "5.6 Header names [lex.header]") "

[h-char-sequence:](#nt:h-char-sequence "5.6 Header names [lex.header]")  
[*h-char*](#nt:h-char "5.6 Header names [lex.header]") [*h-char-sequence*](#nt:h-char-sequence "5.6 Header names [lex.header]")opt

[h-char:](#nt:h-char "5.6 Header names [lex.header]")  
any member of the translation character set except new-line and U+003e greater-than sign

[q-char-sequence:](#nt:q-char-sequence "5.6 Header names [lex.header]")  
[*q-char*](#nt:q-char "5.6 Header names [lex.header]") [*q-char-sequence*](#nt:q-char-sequence "5.6 Header names [lex.header]")opt

[q-char:](#nt:q-char "5.6 Header names [lex.header]")  
any member of the translation character set except new-line and U+0022 quotation mark

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lex.tex#L715)

The sequences in both forms of [*header-name*](#nt:header-name "5.6 Header names [lex.header]")*s* are mapped in animplementation-defined manner to headers or to
external source file names as specified in [[cpp.include]](cpp.include "15.3 Source file inclusion")[.](#1.sentence-1)

[*Note [1](#note-1)*:

Header name preprocessing tokens appear only within
a #include preprocessing directive,
a __has_include preprocessing expression, or
after certain occurrences of an import token
(see [[lex.pptoken]](lex.pptoken "5.5 Preprocessing tokens"))[.](#1.sentence-2)

— *end note*]

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lex.tex#L727)

The appearance of either of the characters ' or \ or of
either of the character sequences /* or // in a[*q-char-sequence*](#nt:q-char-sequence "5.6 Header names [lex.header]") or an [*h-char-sequence*](#nt:h-char-sequence "5.6 Header names [lex.header]") is conditionally-supported with implementation-defined semantics, as is the appearance of the character" in an [*h-char-sequence*](#nt:h-char-sequence "5.6 Header names [lex.header]")[.](#2.sentence-1)

[*Note [2](#note-2)*:

Thus, a sequence of characters
that resembles an escape sequence can result in an error, be interpreted as the
character corresponding to the escape sequence, or have a completely different meaning,
depending on the implementation[.](#2.sentence-2)

— *end note*]