Just point out differences between your races and classes and PHB races and
classes.
I'm building a stand-alone product under the OGL -- I'm not producing under the d20 license, so while I could refer to the Dungeons & Dragons product line and say the product is "for use with D&D" provided I used appropriate disclaimers, in doing so, I'd leave the safe harbor of the d20 trademark license.
So, not for me this time around.
Either I'll acquire some OGC for this or I'll just draft it myself. It's not rocket science to come up with race/class flavor text, but I just felt no need to reinvent a competently built wheel.
Lee
