Date: 2023sep11 Language: C/++ Q. Win32: SAL annotation (source-code annotation language) A. These are macros that help the compiler check function prototypes. In SAL2 they became mixed case:

_In_ // Data is passed to the called funtion (`const`) _Out_ // The caller only provides space for the called function to write to _Inout_ // Usable data is passed into the function and potentially is modified. _Outptr_ // The value that's returned by the called function is a pointer.

There are many others but those are the important ones Older names:

__in became _In_ __out became _Out_ __inout became _Inout_ No earlier equivalent of _Outptr

More info https://www.google.com/search?q=microsoft+SAL+source-code+annotation+language