20 Library introduction [library]

20.3 Definitions [definitions]

20.3.11 handler function [defns.handler]

a non-reserved function whose definition may be provided by a C++ program
[Note: A C++ program may designate a handler function at various points in its execution by supplying a pointer to the function when calling any of the library functions that install handler functions (Clause [language.support]). end note]