Moving between form fields: there and back

I think many more or less pro­sunuti people, as we say in Ukraine (savvy, that is), know that the Tab key moves you to the next field of a form, when you’re fill­ing in a ques­tion­naire, say, or sign­ing up for yet another social network.

But I recently dis­cov­ered, com­pletely by acci­dent, that you can also move to the pre­vi­ous field by hold­ing Shift+Tab.

A useful thing, IMHO. Though I’m not used to it yet.