Add support for margin notes

[tsmyre]

Manifold currently presents Texts only within the confines of a single column, with discursive or bibliographic annotations appearing later in the Text section or in another section completely.

However, there are situations where rendering text side-by-side is critical to the reader experience: as a means to present an elegant solution for online footnotes, a way to present competing or conversant texts in parallel, a strategy for translations that include both original and translated material together. I suspect as we continue to work more in the OER space, the reasons for having the ability to render margin notes will continue to grow.

In Slack we spoke of a possible strategy to address this:

We could build support for something like <span class="marginnote"> into Manifold.

We have a framework in place for doing that—it’s similar to what we’re doing for the H5P stuff.

The expectation would be a publisher could associate one or more “margin paragraphs” with a core body paragraph and that the margin content would sit beside that core paragraph in the reader. Design wise that might be a new drawer or something more like what you would get from a Flexbox approach.

The hope would be that any margin content would, like the core text, be available to highlight, annotation, etc.