<details> element clarifications

Hi guys,

I'm writing an article about <details> element polyfil and after reading
the specification at
http://www.w3.org/html/wg/drafts/html/master/interactive-elements.html#the-details-element
want to clarify some parts in it.

*The first summary element child of the element, if any, represents the
summary or legend of the details. If there is no child summary element, the
user agent should provide its own legend (e.g. "Details").*

1)

The first definition of <summary> assumes that it may NOT be the first
child of <details>. Later, I found a correction at
http://www.w3.org/html/wg/drafts/html/master/interactive-elements.html#the-summary-element
:

*Contexts in which this element can be used:*
*As the first child of a details element.*

So what's the correct answer then? Is it valid for the <summary> element
not to be the first child?As far as I see in Webkit implementation allows
that.

2)

What's the goal of adding fake "Details" legend if <details> does not
contain a child <summary>? It's a bit weird so I'd like to understand this
edge case better to be as much complied to the spec as possible.

Thanks!

---
Maksim Chemerisuk