Can we remove support for some types of `newContent`?

[botandrose]

Right now, the newContent argument passed to the main morph function can be a dizzying array of types:

• Element
• Node
• HTMLCollection
• Array<Node>
• string
• null

Also, for the first 4 types, newContent may or may not be already attached to the DOM, which opens the possibility of additional complications. It could conceivably have hidden state, or have siblings that we don't want to morph, etc.

Can we pare this possibility space down at all, and safely support less use-cases?

@MichaelWest22 has already done some exploration about this in branches:
https://github.com/MichaelWest22/idiomorph/tree/fix-outer-normalize
https://github.com/MichaelWest22/idiomorph/tree/fix-outer-normalize2

[botandrose]

Just noticed this in the README:

Note that [Idiomorph.morph] is a destructive operation with respect to both the existingNode and the newNode.

This isn't true anymore, at least in that newNode is now preserved, largely to ensure that the callback arguments are called with the correct values. But it does indicate that maybe we can at least reparent newNode if necessary.