# Rationale

## Locales

Locales have a very close relation to string processing. They contain information about the character sets and are used, for example, to change the case of characters and to classify the characters.

C++ allows to work with multiple different instances of locales at once. If an algorithm manipulates some data in a way that requires the usage of locales, there must be a way to specify them. However, one instance of locales is sufficient for most of the applications, and for a user it could be very tedious to specify which locales to use at every place where it is needed.

Fortunately, the C++ standard allows to specify the global locales (using static member function `std:locale::global()`). When instantiating an `std::locale` class without explicit information, the instance will be initialized with the global locale. This implies, that if an algorithm needs a locale, it should have an `std::locale` parameter defaulting to `std::locale()`. If a user needs to specify locales explicitly, she can do so. Otherwise the global locales are used.

## Regular Expressions

Regular expressions are an essential part of text processing. For this reason, the library also provides regex variants of some algorithms. The library does not attempt to replace Boost.Regex; it merely wraps its functionality in a new interface. As a part of this library, regex algorithms integrate smoothly with other components, which brings additional value.