0 space to superview but still have gap between them in Xcode

Question

I drap a Text View into one viewController in storyborad and set 'auto layout' which make this textView to be 0 top ,0 leading ,0 trailing to its superview. But why still there're gap(8 pixel about) on left and right respectively between them? In outline document there's top(and bottom) layout guide,are they the guilty?

Answer 1

Uncheck "Constrain to margins" in the pin menu (bottom right of storyboard)