What are the fields in the storyboard, and why does the iPhone 6 plus have different side margins than other iPhones?

Question

When creating constraints in my views in Xcode 6, I noticed this default constrained field, which is checked by default:

The result of saving this flag is that the application will work fine on all iPhones, except the iPhone 6 Plus, where I will have several fields to the left and right of the view:

I tried looking at the Apple documentation, but maybe not that hard. What is margin in Xcode 6 and above? Why is margin only on the sides and not on the top / bottom? And why is it only the iPhone 6 Plus has this margin? Why not iPhone 6 and others? Are these fields described somewhere?

Answer 1

You need to click “relative to the field” in the attributes of the horizontal space constraint