Complex documents in edlib
One of my core goals in developing edlib is to allow the display to be programmatically controlled: the content of a document is formatted dynamically as it is displayed, and so can respond to context (e.g. location of "point" can modify appearance more than just by displaying a cursor) and also so that the entire document doesn't need to be rendered into a buffer, just the parts being displayed.
A natural (for me) extension to this idea was the possibility that the source of the display wasn't just one single document - multiple documents could be blended. Various examples have occurred to me, though few have been implemented.