Bottomless Rich Edit Controls
Your application can resize a rich edit control (CRichEditCtrl) as needed so that it is always the same size as its contents. A rich edit control supports this so-called "bottomless" functionality by sending its parent window an EN_REQUESTRESIZE notification message whenever the size of its contents changes.
When processing the EN_REQUESTRESIZE notification message, an application should resize the control to the dimensions in the specified REQRESIZE structure. An application might also move any information near the control to accommodate the control's change in height. To resize the control, you can use the CWnd function SetWindowPos.
You can force a bottomless rich edit control to send an EN_REQUESTRESIZE notification message by using the RequestResize member function. This message can be useful in the OnSize handler.
To receive EN_REQUESTRESIZE notification messages, you must enable the notification by using the SetEventMask member function.