With this post, I'm going to go into more detail about the architecture of Operator. To start out, we need to get on the same page with regards to terminology.
In the context of Operator each microformat has handlers associated with it. These handlers are the connections to various services. For instance, the tag microformat has handlers for flickr, delicious, technorati, and upcoming.org. Handlers are have nothing to do with the toolbar per say, they are associated with the microformat itself. Any user interface element could be used to invoke a handler on a microformat.
Actions are a concept specifically associated with the toolbar at this point in time. An action is the pairing of a microformat with a handler in the user interface. For instance, if I pair the geo microformat and Google Maps handler, I have an action that looks up a location on Google Maps based on the content of the geo microformat.
So all that being said, I chose the toolbar as the user interface metaphor because I thought it was a good starting point. I see no reason why my architecture can't be extended for other metaphors.
I invite comments to this post as to other user interface metaphors that could be used for microformats discovery.
Coming in my next post - why on earth did I put Live Clipboard support in Operator? And for that matter, what is Live Clipboard?