What is the correct procedure to trust a key locally in GPG Keychain 1.4.5?

The article on signing keys sounded like a good place to start, but it describes a GUI that no longer seems to exist. For example, there is no “Local signature” checkbox any more. Does this mean that GPG Keychain now considers all signatures to be local by default or does it mean that the ability to locally sign a key has been moved elsewhere?

Generally speaking, considering how serious the implications of changing Ownertrust are, it seems dangerous to offer Ownertrust changes through a simple, readily available pop-up menu in the Details drawer, and to bury something as routine as marking a key as marginally trusted in a menu of options…

I am sure the current interface was not arrived at by accident, however, and should be interested to hear how the developers would like users to mark keys as marginally and cursorily trusted for their local use, without committing publicly to it.