COM and Unicode Guidelines

Because Microsoft Active Accessibility is based on COM, developers need a moderate level of understanding about COM objects and interfaces and must know how to perform basic tasks (for example, how to initialize the COM library). Server developers need to understand how to design classes that implement the IAccessible interface and how to create accessible objects.

You also need a moderate level of understanding about Unicode to use many of the Active Accessibility functions that return strings.

To use Active Accessibility effectively, you should understand the following COM and Unicode functions, structures, data types, and interfaces.

Functions	OleInitialize CoInitialize AddRef and Release VariantInit and VariantClear MultiByteToWideChar and WideCharToMultiByte SysAllocString and SysFreeString
Structures and data types	VARIANT HRESULT BSTR
COM interfaces	IUnknown IDispatch IEnumVARIANT

Limited information about some of these items is provided in this documentation. For a description of standard COM parameter attributes [in], [out], [in/out], and [out, retval], see Definitions of Parameter Attributes.