Code for creating custom sidebars and then selecting one on a given post...

[drywall]

Also cleaned up some minor E_NOTICE-level PHP errors on the normal sidebar handling.

The execution of this on the Theme Options page isn't super-elegant — it's just a textarea with each custom sidebar needing to go on a separate line — but the Theme Options Framework doesn't really have any better field type to use for this.

Works fine, though. Post authors only get to choose from the custom-defined sidebars from the Theme Options page, which should mean only the sorts of folks you'd want to have the power to create new sidebars can do so.

[aschweigert]

This looks good for the most part. Two things:

I think the way this should work is that it would use the custom sidebar instead of rather than in addition to the sidebar that would otherwise be displayed on that page. So...we should move the test for whether the custom sidebar exists up into the other logic in sidebar.php (that might require a little bit of rethinking how that's organized).

And then #2 is that I think instead of using "none" as the first option in the dropdown in the post/page meta box we should use "default" (even if that doesn't really do anything other than just make it clear to the other what will appear. "None" seems a bit problematic because as an author I might read that as show no sidebar at all and then think I have to pick one of the custom options.

Otherwise I think this is pretty much good to go!