boost-react-native-bundle/boost_1_57_0/libs/locale/doc/collation.txt

Boost library as in https://sourceforge.net/projects/boost/files/boost/1.57.0/

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//  Copyright (c) 2009-2011 Artyom Beilis (Tonkikh)
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//  Distributed under the Boost Software License, Version 1.0. (See
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/*!
\page collation Collation 

Boost.Locale provides a \ref boost::locale::collator "collator" class, derived from \c std::collate, that adds support for
primary, secondary, tertiary, quaternary and identical comparison levels. They can be approximately defined as:

-# Primary -- ignore accents and character case, comparing base letters only. For example "facade" and "Façade" are the same.
-# Secondary -- ignore character case but consider accents. "facade" and "façade" are different but "Façade" and "façade" are the same.
-# Tertiary -- consider both case and accents: "Façade" and "façade" are different. Ignore punctuation.
-# Quaternary -- consider all case, accents, and punctuation. The words must be identical in terms of Unicode representation.
-# Identical -- as quaternary, but compare code points as well.

There are two ways of using the \ref boost::locale::collator "collator" facet: directly, by calling its member functions \ref boost::locale::collator::compare() "compare", \ref boost::locale::collator::transform() "transform" and \ref
boost::locale::collator::hash() "hash", or indirectly by using the \ref boost::locale::comparator "comparator" template
class in STL algorithms.

For example:

\code
    wstring a=L"Façade", b=L"facade";
    bool eq = 0 == use_facet<collator<wchar_t> >(loc).compare(collator_base::secondary,a,b);
    wcout << a <<L" and "<<b<<L" are " << (eq ? L"identical" : L"different")<<endl;
\endcode

\c std::locale is designed to be useful as a comparison class in STL collections and algorithms.
To get similar functionality with comparison levels, you must use the comparator class.

\code
    std::map<std::string,std::string,comparator<char,collator_base::secondary> > strings;
    // Now strings uses the default system locale for string comparison
\endcode

You can also set a specific locale or level when creating and using the \ref boost::locale::comparator "comparator" class:

\code
    comparator<char> comp(some_locale,some_level);
    std::map<std::string,std::string,comparator<char> > strings(comp);
\endcode

*/