A memory object on the clipboard can be in any data format, called a clipboard format. Each format is identified by an unsigned integer value. For standard (predefined) clipboard formats, this value is a constant defined by the Microsoft® Win32® API; for registered clipboard formats, it is the return value of the RegisterClipboardFormat function.
Except for registering clipboard formats, individual windows perform most clipboard operations. Typically, a window procedure transfers information to or from the clipboard in response to the WM_COMMAND message.
The clipboard is user-driven. A window should transfer data to or from the clipboard only in response to a command from the user. A window must not use the clipboard to transfer data without the user's knowledge.