Juan Picado (18) [Avatar] Offline
Here you says Flexbox is Chapter 8 but I guess you meant Chapter 5, ( at least in the V3).

There is a lot you can do with flexbox. If you have looked into learning it before, you have probably seen daunting examples that use as many as a dozen different properties. We’ll dive deeper into all those options in Chapter 8, but to start, you don’t need all that. This example shows all you need to build your first flexbox-based layout. (IE10 requires some vendor- prefixed properties as well; I’ll also address that in Chapter smilie.

Also here

Can you use flexbox? (i.e. You don't need to support IE9) Flexbox can center your content. See chapter 8.
Keith J Grant (27) [Avatar] Offline
I re-arranged the chapter order at one point. Thanks for catching those. I'll update the text