A rich edit control's parent window can process notification messages to monitor events affecting the control. Rich edit controls support all of the notification messages used with edit controls as well as several additional ones. You can determine which notification messages a rich edit control sends its parent window by setting its event mask.
To set the event mask for a rich edit control, use the EM_SETEVENTMASK message. You can retrieve the current event mask for a rich edit control by using the EM_GETEVENTMASK message.
A rich edit control's parent window can filter all keyboard and mouse input to the control by processing the EN_MSGFILTER notification message. The parent window can prevent the keyboard or mouse message from being processed or can change the message by modifying the specified MSGFILTER structure.
An application can process the EN_PROTECTED notification message to detect when the users attempts to modify protected text. To mark a range of text as protected, you can set the protected character effect. For more information, see Text Formatting.
You can enable the user to drop files in a rich edit control by processing the EN_DROPFILES notification message. The specified ENDROPFILES structure contains information about the files being dropped.