New 3.18 feature

[Thomas SIMON]

Dear all,

Would somebody be able to help me figure out what one new icon (in Gnome
3.18, it appeared after upgrade using staging ppa) is for? It is visible
in the following link:

https://help.gnome.org/users/gnome-help/stable/shell-introduction.html.en#yourname

The aforementioned icon is the one that is between settings and lock,
the second starting from the left. On my laptop (Lenovo Yoga) it looks a
bit like a tablet inclined at 45° and clicking it changes the bottom
left corner from a turning arrow to a lock. 

So I guessed it would be to rotate / block rotate of the screen but that
does not seem to be working.

Regards,

Thomas