Why does the screen size half when I long press the Windows button in WP10?

[AforAkshay]

Long pressing windows button in wp10!

I own a lumia 540 and just got developer preview of windows 10 on my mobile yesterday. When I long press the home button or windows button, the screen size is halved!
The start screen goes to lower half part of the screen and upper half remains black.
I couldn't figure out what is it?
Anyone of you encountered anything similar?
And know what is it? Some sort of multi window thing or what?

 

[jjmorgan64]

re:

It's to reach the top of the screen Onee handed

 

[Harrie-S]

re:

Yes because that is an added feature.
So with that you can use "one hand" to "reach" something on the top of the screen.

 

[RumoredNow]

re:

Moved to appropriate forum...

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