Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. — Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

Constructor.

constexpr
ignore_case_param(
    implementation-defined);

Construction from ignore_case indicates that comparisons should be case-insensitive.

When ignore_case is passed as an argument, this function ignores case when performing comparisons:

void f( ignore_case_param = {} );