Where is this "overflow menu button" in Android Studio?

Question

According to a tip here, one can simultaneously view a layout in Android in various screen sizes and orientations. It says, "Click on the overflow menu button > Preview All Screen Sizes. You can switch between landscape/portrait orientations too."

"Whey cool!" I thought, while serendipitously sitting on my tuffet.

But when I brought up Droidio (Android Studio), and a layout/*.xml file in Design mode, I sought in vain for any trace of "Preview All Screen Sizes". I then realized that I had misread the statement -- I had at first translated "overflow menu button" in my mind as the context menu. So...what is the "overflow menu button" and where is it?

Here's what I see:

Answer 1

Click where it says 'Nexus 4' - at the bottom of the list of devices is the Preview All Screen Sizes option.