//
// Copyright (c) 2023 Alan de Freitas (alandefreitas@gmail.com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at https://www.boost.org/LICENSE_1_0.txt)
//
// Official repository: https://github.com/boostorg/url
//


[#grammar]
= Customization

For a wide range of applications the library's container interfaces
are sufficient for URLs using the generic syntax or the well known
schemes. There are however more complex cases where it is desired
to go beyond what the library offers:

* Create new custom containers for other schemes
* Incorporate the parsing of URLs in an enclosing grammar
* Parse https://tools.ietf.org/html/rfc3986[rfc3986,window=blank_] elements in non-URL contexts
  (`authority_view` is an example of this).
* Define new ABNF rules used to parse non-URL strings

To enable these use-cases, the library provides a suite of general
facilities for processing low-ASCII character strings, and makes
public the interface to useful rules found in rfc3986. The design
goals of these facilities are:

* No use of cpp:std::locale[] or cpp:std::char_traits[]
* No exotic character types, just low-ASCII `char`
* No memory allocation (or bounded allocation)
* Flexible composition with non-terminal rules
* Optimized for the grammars commonly found in RFCs
* Easily extended by downstream consumers

The general facilities are nested in the fully qualified namespace
`boost::urls::grammar`, while the headers for rfc3986-specific parsing
algorithms are located in the `<boost/url/rfc/>` include directory.
This section explains the design and use of the general facilities
to define and parse new grammars.

== Syntax Notation

The documentation and reference for this library use the
Augmented Backus-Naur Form
(https://datatracker.ietf.org/doc/html/rfc2234[ABNF,window=blank_])
notation throughout to specify grammar rules. An
understanding of this notation is necessary to achieve
best results for learning how to use the custom parsing
features.

[NOTE]
====
Code samples and identifiers in this customization
section are written as if the following declarations
are in effect:

[source,cpp]
----
#include <boost/url/grammar.hpp>

using namespace ::boost::urls::grammar;
----

====