“The shape() function uses a set of commands roughly equivalent to the ones used by path(), but does so with more standard CSS syntax, and allows the full range of CSS functionality, such as additional units and math functions.” So it’s paths redefined in a CSS native syntax.

That just shows that paths should not be limited to the SVG spec but live and prosper on its own and be able to be expressed in alternative ways

keep reading the spec until the example ... it's not only path expressed differently. Shape can be built using variables, calc, different units, math functions, etc etc ... path uses numbers that are nothing but hard-coded pixel values. This makes a huge difference.

And is probably something that would be good outside of CSS as well? Anyhow, as I said, I’m sorry