After Effects Tapered Stroke: No plugins, no expressions!

This has come up repeatedly on various forums and discussions (probably because I think text layers are the answer to everything), and today I decided I was tired of explaining it in written form. I have a much longer and more in-depth demo which I've done live, and also as a tutorial for School of Motion, available here: https://www.youtube.com/watch?v=plbsdkRhy8g I did a month of daily experiments using related techniques in January 2019: https://kylehamrick.com/textperiments-1. (Includes link to a pay-what-you-want project file with tons of ideas.)