Well, GetWindowLong and SetWindowLong are Win32 API functions and are not built-in in JScript. Therefore, you'll need to call the libraries with Interop.Call. Also, the control handle can only be retrieved with PlusWnd.GetControlHandle. With these two things in mind, we end up with the following code:
code:
//PlusWnd is your created window with the RichEditControl
var GWL_EXSTYLE = -16
var WS_EX_TRANSPARENT = 0x20
var hWnd = PlusWnd.GetControlHandle("EdtThingy"); //Parameter is the Id of the RichEditcontrol
var Style = Interop.Call("user32", "GetWindowLong", hWnd, GWL_STYLE);
if(Style > 0) {
Interop.Call("user32", "SetWindowLong", hWnd, GWL_STYLE, Style | WS_EX_TRANSPARENT);
} else {
Debug.Trace("GetWindowLong returned an error. Return value: "+(Style.toString()));
}