20 Library introduction [library]

20.3 Definitions [definitions]

20.3.21 required behavior [defns.required.behavior]

a description of replacement function and handler function semantics applicable to both the behavior provided by the implementation and the behavior of any such function definition in the program
[Note
:
If such a function defined in a C++ program fails to meet the required behavior when it executes, the behavior is undefined.
end note
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