About CSS Flexible Box Layout Module Level 1 :
https://www.w3.org/TR/css-flexbox-1/#flex-property

I think there's an error on Flexbox spec about flex shorthand initial value: it is set to "1 0 auto", but actually should be "0 1 auto" since:

• flex-grow initial value is 0
• flex-shrink initial value is 1
• flex-basis initial value is auto