Author here (of the plugin, not the page).

This was my only tangible contribution to the Gimp, some twenty years ago. IIRC it was modelled after a similar feature in Paint Shop Pro, and it was easy enough an exercise for an aspiring programmer. Or so I thought: others have now spent much more time maintaining it than I spent writing it.

In hindsight it seems like a bizarre idea to have a feature whose GUI requires filling in 25 numbers. But perhaps it has use as an educational tool.

In development version of the Gimp, the entire plugin has effectively been rewritten. Good riddance!