Makes sense Aldo, glad you where around to intervene before I sent Talwyn on a short-wavelength visible-light Clupea Pallasii pursuit.

As a minor suggestion if you ever get around to re-writing any of the code:

With the Get/SetWindowLong() calls you could inspect the index parameter and adjust it internally to allow users to add their own window words without colliding with yours. Say for example you are using 10 words internally, you could add ten to the user supplied index on the way through to calling the native API's and if anyone needs to access YOUR window words, they could use the negative offset convention in the same way as these are used by the underlying API's for their internal stuff.

In that way, you still provide access to the full API but protect your internals from fools like me:)