Give the user indication that the UI has been hidden (and how to get it back)

[GarryP]

It seems like we get something like one post per week where the user has ‘lost their tools’ which, usually, is caused by them pressing TAB accidentally.
Since:
* it’s so easy for someone to press TAB accidentally;
* it’s not something that all users would expect to happen;
* there is no on-screen indication of what has happened or how to undo what’s happened...
… I would like to recommend that some kind on on-screen indication is given to the user to tell them how to get the UI back.

On Windows this could be achieved by having some simple wording in the window title bar, such as “[UI has been hidden - press TAB to reveal it]” (see attached mock-up) but I don’t know if this can be achievable on OS X or iPad.

Alternatively a message akin to the Assistant pop-ups could appear. The message could have a ‘close’ icon (which has to be pressed to remove it since the user may not see a message that goes away by itself after a second or so as they are ‘in a panic’ because everything has disappeared) with a ‘Don’t remind me again’ checkbox for more experienced users, or something similar.

I’m sure there are other alternatives, and I don’t really have any preference to which is used, but I do think that the user should be given more information about what has happened and how to get the UI back as it can be disconcerting to have things disappear and not know what to do about it.