Added support for multiple editors/toolbars on a page.
Adds a filter-for-export filter:
This formatter walks through the content tree.
At each node it checks if the node implements a method filterForExport
If so, the method is called.
In this way, custom elements can filter out their contents from export.
So if an editor includes an element: <custom-element></custom-element>,
And the custom element sets some content such that inner html looks like:
<custom-element>Content For Display</custom-element>
The prototype for <custom-element> may implement filterForExport thusly:
CustomElement.prototype.filterForExport = function () {
this.innerHTML == '';
}
And the exported html will look like this:
<custom-element></custom-element>
In this way a custom element my render demonstrative content inside the editor, but not have that content saved to our database.