Wow, thanks for posting. I eagerly look forward to these in-depth posts. I imagine there must be not many people in the world interested in this stuff but I'm definitely one of them :-) Overleaf is also uniquely positioned to demystify some of this and improve the user experience for TeX/LaTeX users. (Sorry wanted to comment after I was done but only noticed this on Sunday and didn't finish on the weekend… still reading part 4.)