hi I'm new here and I just wanted to know whether all these rules and the rewritten planescape campaign setting were in 3.5 rules. Thanks 
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Well, there are two parts to the site. The Planescape Campaign Setting (PSCS), found under the Official Products section, was started during the time of 3E but the material is being slowly adapted to 3.5E. You can ask Moogle001 for more details about that.
The second part of the site is "everything else", and that means it can be 1E, 2E, 3E or 3.5E, or even entirely rule-less. We accept a wide range of submissions. That said, we would obviously prefer if people attuned to 3.5E, but since I'm particularly bad at following established rules myself, I can hardly begrudge someone else their right to write in 2E.