[yorwba]

Maybe the ELI5 plugin could be reasonably approximated by adding links to all phrases with corresponding Wikipedia articles, like:

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

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

https://en.wikipedia.org/wiki/N-simplex

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

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

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

I guess it depends on whether you're willing to read a textbook's worth of Wikipedia articles. (There is no shortcut. Actual 5-year-olds also require a few years until they can understand advanced mathematics.)