specification list doesn't indicate that it's showing a subset

This page

  https://launchpad.net/products/bzr/+specs

apparently lists all bzr specifcations, or at least so I would surmise from the url and the contents of the page. However, it apparently only shows specifications that are not yet implemented.

That's a fine default; specifications which are already implemented are generally less interesting. However it should be more obvious that this is the case.

Suggested solution: near the top of the field have some links which toggle between:

  Unimplemented | Active | Obsolete | All

or some similar classifications.

There's actually a common pattern here of choosing a subset of a particular group of objects. For example, a person's bugs that were reported/assigned/subscribed/etc. At the moment these are put over in the right-hand navigation box, which mixes them in with actions that can be taken, and makes it much less clear which one is currently selected.