Ever want to search on a particular phrase but only want to bring back documentation or blogs, or news, or store results? It seems Google is testing this option now for some users (I do not see it).
A Search Engine Watch Forum thread named Google Refinement Keywords shows this in action. This person search on Cookies (link to screen capture) and was presented with refinement options, including, Blogs / Troubleshooting / News / Stores / Documentation / Recipes (links to screen captures).
It looks like it changes the query to cookies more:blogs which doesn't change anything on my SERPs.
Danny Sullivan thought this may be how Google Base works, but it seems to be simpler then that. This can be useful, in my opinion.
Forum discussion at Search Engine Watch Forums.
