Draws a rectangle in the style used to indicate that the rectangle has the focus.
Since this is a Boolean XOR function, calling this function a second time with the same rectangle removes the rectangle from the display. The rectangle drawn by this function cannot be scrolled. To scroll an area containing a rectangle drawn by this function, first call DrawFocusRect to remove the rectangle from the display, then scroll the area, and then call DrawFocusRect again to draw the rectangle in the new position.
DrawFocusRect works only in MM_TEXT mode. In other modes, this function does not draw the focus rectangle correctly, but it does not return error values.