Add support for multi-line footnotes and image footnotes in Gutenberg

Creating multi-line tooltips in Gutenberg with this plug-in is too much of a hassle. When I press “Enter” in Gutenberg, it creates a new block, and so the footnote shortcode won’t work. I had to press “shift-enter” to create another line.

The problem is similar when trying to put images inside the footnote using Gutenberg. I had to use the classic editor block just to get the plugin to properly contain the image inside the tooltip.

I really like this plugin, but it would be nice if you can make it more Gutenberg-friendly, especially since the Classic editor is gonna be phased out soon.