The MSGFILTER structure contains information about a keyboard or mouse event. A rich edit control sends this structure to its parent window as part of an EN_MSGFILTER notification message, enabling the parent to change the message or prevent it from being processed.
typedef struct _msgfilter { NMHDR nmhdr; UINT msg; _WPAD _wPad1; WPARAM wParam; _WPAD _wPad2; LPARAM lParam; } MSGFILTER;