Dumb question for a 12-year user of Textmate (we missed the 10-yer anniversary, it seems: happy birthday TM!), but…

How is the project folder determined? Specifically, I’ve got a tab open which is in a folder marked in the filebrowser (^⌥⌘-D) as the project folder (at least ) it’s ticked in the little drop down menu (see image).

But… If I ⇧⌘-F (find in project), the Dropbox folder is selected… What determines what is set when one used command-shift-F?

In general, I’d appreciate if anyone has pointers to a decent tutorial on how to use project folders.