Projects Perspective

I’m probably missing something really obvious here, but is it possible to create a perspective with a few selected projects/folders?

I know you can focus on one project in a perspective by adding it with the “Add Focus” button in the perspectives window. I seems as if you should be able to add more than one project/folder to a given perspective, but the “Add Focus” button greys out after I add a single project focus.

Does anyone know?

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Okay, nevermind. I figured it out. You have to choose a second item from the dropdown box before it will work.