[caution: possible thread drift ahead]
I'm confused here. Isn't the (stated) purpose of this message to render RichEdit text on a device (presumably a printer) in a WYSIWYG manner?
If so, then how could it possibly only work on a NULL DC? Is the MSDN documentation totally off here?
Here's one of Raymond Chen's blog entries in which he explains how to print RichEdit text. His code uses this message for its stated purpose. (Of course, this was written in 2007; maybe things have changed since then?) So maybe there's the intended behavior
and the undocumented functionality.
Also, I looked at that ReactOS page and I'm really curious: what exactly is that project? They seem to be examining stuff in the OS to see if it works or not, or maybe I'm missing something here. (Hmm; maybe it has something to do with
Doxygen. But then, what is that? something about "Generat[ing] documentation from source code".)
Anyhow, if
EM_SETTARGETDEVICE works for you to toggle word-wrapping in a RichEdit control, then I'm game to try it.