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;