[#boost-urls-grammar-hexdig_chars]
= xref:boost.adoc[boost]::xref:boost/urls.adoc[urls]::xref:boost/urls/grammar.adoc[grammar]::hexdig_chars
:relfileprefix: ../../../
:mrdocs:

The set of hexadecimal digits

== Synopsis

Declared in `<https://www.github.com/boostorg/url/blob/develop/include/boost/url/grammar/hexdig_chars.hpp#L97[boost/url/grammar/hexdig_chars.hpp]>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
constexpr /* implementation-defined */ hexdig_chars = {};
----

== Description

== Example
Character sets are used with rules and the functions xref:boost/urls/grammar/find_if.adoc[`find_if`] and xref:boost/urls/grammar/find_if_not.adoc[`find_if_not`].

[,cpp]
----
system::result< core::string_view > rv = parse( "8086FC19", token_rule( hexdig_chars ) );
----
== BNF
[,cpp]
----
HEXDIG      = DIGIT
            / "A" / "B" / "C" / "D" / "E" / "F"
            / "a" / "b" / "c" / "d" / "e" / "f"
----
[NOTE]
The RFCs are inconsistent on the case sensitivity of hexadecimal digits&period; Existing uses suggest case&hyphen;insensitivity is a de&hyphen;facto standard&period;

== Specification
* https://datatracker.ietf.org/doc/html/rfc5234#appendix-B.1[]
* https://datatracker.ietf.org/doc/html/rfc7230#section-1.2[]
* https://datatracker.ietf.org/doc/html/rfc5952#section-2.3[]
* https://datatracker.ietf.org/doc/html/rfc5952#section-4.3[]

== See Also

xref:boost/urls/grammar/find_if.adoc[`find&lowbar;if`], xref:boost/urls/grammar/find_if_not.adoc[`find&lowbar;if&lowbar;not`], xref:boost/urls/grammar/hexdig_value.adoc[`hexdig&lowbar;value`], xref:boost/urls/grammar/parse-09.adoc[`parse`], xref:boost/urls/grammar/token_rule.adoc[`token&lowbar;rule`]&period;


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