I once took a stab at rewriting it in C99 using reference counting for memory management [2], so I recognised the screenshot in Kosmonaut immediately.

Unfortunately the article series stops before explaining inline layouts and I never got around to doing anything further with my implementation.

[1] https://limpet.net/mbrubeck/2014/08/08/toy-layout-engine-1.h...

[2] https://github.com/wernsey/robinson-c