In typography, a "runt" is a short line at the end of a paragraph. Typographers generally try to avoid runts. I've added two examples that use the Prince Boxtracking API to avoid runts. The first example reduces "letter-spacing" in runt-infested paragraphs:

https://css4.pub/2024/boxtracking/#avoiding-runts

The second example uses variable fonts to narrow the glyphs so that more letters will fit on a line:

https://css4.pub/2024/boxtracking/#avoiding-runts-with-variable-fonts

To make variable fonts work on your own computer, you will need a recent version of Prince:

https://princexml.com/latest

The techniques used is also known as microtypography:

https://en.wikipedia.org/wiki/Microtypography

This is work in progress, use with care.

Edited 29 Dec 2024 by howcome