In a .pdf?

In seriousness, I think this kind of extreme highlighting could be an important step in making programming more accessible. There are only so many characters like ,;:.()[]{}<> available to use in code, and often most of them indicate completely different things in different places.

Done the right way, and combined with live evaluation á la Bret Victor or the Swift playground, I think this has the potential to be the next paradigm of accessible programming, after Excel.