[css3-flexbox] does flex-order impact stacking order of overlapping content

Hi www-style,

In the current Flexbox ED "Layout Algorithm" section, it says this about 
flex-order:

 > Re-order the flexbox items according to their ‘flex-order’.
[...]
 > This affects the order in which the flexbox items generate
 > boxes in the box-tree

Given that -- hypothetically, if two flexbox items were to contain 
overlapping content[1], would flex-order have any effect on which one 
overlaps the other? (i.e. does flex-order affect stacking in the z axis?)

I've been assuming "no", since (discounting the "z-index" property) 
elements generally stack in the z axis according to *document order*. 
So, since flex-order is independent of document order, I wouldn't expect 
it to affect stacking in the z axis.

Just wanted to clarify, though, because "the order in which flexbox 
items generate boxes in the box tree" sounded like it might impact 
stacking-order.

Thanks,
~Daniel

[1] I'm not 100% sure that it's even possible to get overlapping content 
in different flexbox-items, but I'm guessing it might be doable with 
"position:relative" or something.