Editing footnotes

This example demonstrates one way to implement something like footnotes in ProseMirror. The footnotes in this editor's schema are inline nodes which contain inline content. They are drawn in the editor as numbers, but when you node-select them, they pop up a little sub-editor. Changes in this sub-editor are propagated to the outer editor, and vice versa, so that collaborative editing would work even for the footnote text.

The source code for this example can be found on github.