support pushfirst!(parent::Node, child::Node)

[guo-yong-zhi]

No description provided.

[guo-yong-zhi]

And can we have emptychildren!(parent::Node)?
If you don't want to add too many proxy api for children,
should we allow people to do something like func!(parent.children)?
Or, func!(children(parent))? (Promise that the children(parent) return a reference when it's not empty)
Or, func!(children!(parent))?

[joshday]

I think we could just let empty!(::Node) perform the action of emptying the children Vector.

My idea here is that a Node should act like a Vector in regards to children and act like a (mutable) NamedTuple in regards to attributes.

[guo-yong-zhi]

but... how to empty! its attributes?