Attributes Inspector: how to use "Stretching"

Question

What are the numbers in the Stretching box in the View sub-box Interface Builder's Attributes Inspector?

(as a side question - I suppose a respectable company such as Apple would have actually released documentation for its tools, as opposed to letting developers just guess everything; so, where's this documentation?...)

Answer 1

This blog post Karol seems to explain it pretty well. - http://macoscope.com/blog/stretchable-images-using-interface-builder/

Stretching properties are pretty simple (I don't think so, but the articles does :).

The fraction of the original image left without stretching on the left is specified by X The fraction of the original image that gets stretched in the x-axis is specified by Width The fraction of the original image left without stretching on the right is equal to 1 – X – Width If we use 0 for Width the stretched area will interpolate between the last pixel of the left part and the first pixel of the right part The y-axis works analogously

Answer 2

Viewing a .storyboard file in a text editor (figures it's an XML file) revealed the answer: it is linked to UIView's contentStretch property.