Add in-code comments where helpful

[patrickmj]

For this project (and generally, IMHO), in-code comments should be used primarily for detailed explanation of how something complicated works. Rule of thumb is that if it takes more than 15 minutes to figure out, or if you did research to find a solution, those should be in the in-code docs, with links.

Do that in as many places as possible.

If the same idea applies to an entire file or folder, add it as a README (or other markdown file) to the containing folder.