[chrisblizzard]

Hi. I work on Facebook's documentation for developers. It's true that IDs are opaque and I don't think that we declare that anywhere in particular. (It's a known unknown?)

I've updated the Graph API getting started guide to mention the fact that IDs are opaque and also mentioned it in our comments guide since comments are one of the few places where we have IDs that are made up of other keys.

Thanks for the feedback - it's good to hear about things we can fix.