SAL annotations
If you examine the library header files, you may notice some unusual annotations, for example, _In_z and _Out_z_cap_(_Size). These annotations are examples of the Microsoft source-code annotation language (SAL). SAL provides a set of annotations to describe how a function uses its parameters and return type. For example, it indicates the assumptions it makes about them and the guarantees it makes on finishing. The header file <sal.h> defines the annotations.
For more information about using SAL annotations in Visual Studio, see Using SAL annotations to reduce C/C++ code defects.