To clarify (?) my vote (FAQ, errata, published books)...
Errata are corrections to the rules published by WotC in official documents/books. Whether they publish these corrections in the FAQs (as they have done many times), in supplements (like polymorph other in Tome and Blood) or in the regular errata document makes no difference to me with regards to their official nature - they all become part of the "rules as written". It must be presented as a "correction" though (as opposed to a "mistake").
The FAQ and supplements are "unquestionable" sources of rules interpretation when the rules are actually open to interpretation. (And not the "let's pretend the rules don't mean what they say" kind of "interpretation" popular in some circles.) That's fairly rare.
The FAQ and supplements can also add to the rules. For example, I consider the "if you no longer qualify for a prestige class you loose class abilities" rule to be "official".
In a way the Rules of the Game articles are in a similar situation because they too are, technically, published by WotC. I'd give them tentative (but not unquestionable) "right" to interpret, but not to change or to add. They miss out on the "unquestionable" qualifier, and the right to change or add, because as opposed to published supplements or even the FAQs there's no implied assumption that they're based on a general consensus/"peer review" among the people currently responsible for the rules. They're not "official".
Errata are corrections to the rules published by WotC in official documents/books. Whether they publish these corrections in the FAQs (as they have done many times), in supplements (like polymorph other in Tome and Blood) or in the regular errata document makes no difference to me with regards to their official nature - they all become part of the "rules as written". It must be presented as a "correction" though (as opposed to a "mistake").
The FAQ and supplements are "unquestionable" sources of rules interpretation when the rules are actually open to interpretation. (And not the "let's pretend the rules don't mean what they say" kind of "interpretation" popular in some circles.) That's fairly rare.
The FAQ and supplements can also add to the rules. For example, I consider the "if you no longer qualify for a prestige class you loose class abilities" rule to be "official".
In a way the Rules of the Game articles are in a similar situation because they too are, technically, published by WotC. I'd give them tentative (but not unquestionable) "right" to interpret, but not to change or to add. They miss out on the "unquestionable" qualifier, and the right to change or add, because as opposed to published supplements or even the FAQs there's no implied assumption that they're based on a general consensus/"peer review" among the people currently responsible for the rules. They're not "official".