If you were to override `buildChildView` instantiating the childViews with an `el` then you can create a collectionView from pre-rendered DOM

CollectionView can’t be initially “rendered” because it does its initialization of many things on first render.

when a collection view is DOM
* and it's not attached to the document
** should have _isAttached set to false

* and it's attached to the document
** should have _isAttached set to true

when rendering a childView
* should not render childView twice

when a collection view is DOM
* and it's not attached to the document
** should have a child view without `_isAttached`

* and it's attached to the document
** should have a child view with `_isAttached` set to `true`

…view-iso

Allow CollectionView to be populated with pre-rendered DOM

This function removes the need for a `preventDestroy` option.

Essentially if you want to `preventDestroy` just detach the view first. When you want to preventDestroy you already have to have a copy of the view.. and depending on what is doing the view emptying `preventDestroy` can become a round about API.

What you really want is
```js
const myView = myRegion.currentView;
myRegion.detachView();
myOtherRegion.show(myView);
```

* mergeOptions src/common/merge-options.js
* iterate through `keys` and merge instead
  of getting the `keys` from options, then merging

monitor-view-events  src/common/monitor-view-events.js
* Define once:
   triggerDOMRefresh
   handleBeforeAttach
   handleAttach
   handleBeforeDetach
   handleDetach
   handleRender

triggerMethodOn src/common/trigger-method.js
* Distinct if `context` has triggerMethod, use and return result
   with fallback to helper function and return result

CollectionView src/collection-view.js
* private childViewEventHandle for optimization
* _proxyChildEvents using childViewEventHandle

src/common/trigger-method.js
* will remember the last `event` name transform

src/mixins/behaviors.js
takes arraylike value only

src/mixins/view.js
triggerMethod
only passes along `arguments` other functions

* Make trigger on behavior follow same patterns as parent

* Make childViewEventHandler a common module

…arionettejs#3105)

* CollectionView# and CompositeView#

_initialEvents
* Listen to `this.collection~event:update` instead.

_onCollectionUpdate
* pass `options.changed.removed` to `this._removeChildViews`
* updated test to reflect additions

 _removeChildViews
* use array of models to determine what views to remove if not already destroyed.
* Support `checkEmpty` for preventing empty collection checking

_destroyChildren
* checks to see if there are any children to destroy before calling `_removeChildViews`

removeChildView
* using _destroyChildView
* added test for trying to remove falsy and valid values

_getRemovedViews

_removeChildView

- ~~~_onCollectionRemove~~~
* test and references removed

_findGreatestIndexedView
* finds the view with the greatest `_index` and returns it.

_updateIndices
* accepts array of views for _findGreatestIndexedView

[test] when removing the sorted view, the `view._index` should update.

* Attempts to always use models instead of modelOrViews

This may not be helpful.. just wanted to give it one last show.
I don’t think there are perf issues. particularly since `findByModel` is cheap.  In fact I think the complexity of reorder went down.. though I didn’t test it..

detachView
* falsy check

Regions
detachChildView

detachChildView

detachView

[documentation] View#detachChildView

…ChildView

Region detachview detach child view

…marionettejs#3113)

* _createView
* creates view from model and does event monitor and proxyChild events

_renderChildView
* render views and triggers render events

_setupChildView
* sets child view properties:
  parent, _index (conditionally), monitorViewEvents, and  _proxyChildEvents.

* CollectionView

addChildView
* using `_setupChildView`
* triggers `event~before:add:child`
* triggers `event~add:child`
* when buffering, will add view to list of children
  but will not update children length for performance increase
* using `_renderView`

~~_addChildView~~

_updateIndices
* removed need to pass index

_addChild
* removed passing ChildView param
* using `_createView`

_onCollectionAdd
* using `_addChild`

_showCollection
* using `_addChild`
* calls `children._updateLength`

_showEmptyView
* removed unnecessary `view._parent` setting

Make a public detachView

Expose normalizeUIString, to parallel normalizeUIKeys and
normalizeUIValues, issue marionettejs#3174.