The EM_SETTARGETDEVICE message sets the target device and line width used for WYSIWYG (what you see is what you get) formatting in a rich edit control.
EM_SETTARGETDEVICE
wParam = (WPARAM) (HDC) hdcTarget;
lParam = (LPARAM) (int) cxLineWidth;
Parameters
hdcTarget
Handle to a device context for the target device.
cxLineWidth
Line width to use for formatting.
Return Values
Returns a nonzero value if successful or zero otherwise.