<<If the mechanic is partially derived from the SRD, doesn't it have to
be open content?
>>
The OGL says:
"Open Game Content" ... means any work covered by this License, including translations and derivative works under copyright law, but specifically excludes Product Identity."
If you have the authority to designate parts of the product as PI then you can lock them down in spite of the fact that the work, when taken as a whole, is derivative.
By definition, if you include a big chunk of the SRD in your work, your whole work is a derivative work. It may have non-derivative parts, but the work is derivative.
If you couldn't issue PI declarations within the derivative work, then you couldn't even PI your art inside a work that contained a big chunk of the SRD, you'd have to OGC it all.
But clearly, if DC comics creates the Otherworlds medieval Batman game and wants to re-label "Paladin" as "Bat Warrior" then 99.9% of the paladin stuff will be verbatim copied, and the 0.1% (the name) won't be. You are free to PI the value added stuff provided that you can sift it out from the borrowed stuff.
The new, value added components of the product are yours to declare as PI provided that you don't accidentally declare somebody else's OGC as your PI and retroactively lock something down that was open.
Since it's difficult to sift out your content from a predecessor's content when the content becomes mixed, it's generally best to identify all thoroughly mixed content as OGC and PI only non-mixed content.
However, were you careful enough to clearly designate which parts are new compared to which parts are borrowed, you could PI parts of mixed content. Failure to distinguish the value added from the original with clarity, however, would put you in violation of the "clearly" specified OGC requirement.
Since PI can include not only trademarks, but language, themes, concepts, and formatting, almost anything that can be presented in written form is a potential form of PI if you originated it.
I had this opinion early on. Almost nobody agreed. Now quite a few publishers of volumes like the Silhouette Core, Mutants & Masterminds, etc. have all taken up the practice of locking down some things that they perceive to be brand new rules (or at least rules not derived from the SRD directly).
Whether this interpretation is correct or not... only time, and potential litigation may be able to tell.
Lee
