First of all, it's the opposite of Post-Modern, to the perl style do it all in myriads of ways, everything is allowed, OpenSSL style. With Modern, only the best API and implementation is allowed. API's are Stanford style well-planned ahead of time, and not adhoc added New-Jersey style. Changes to the API need a rename, not just a major version bump. Hand-waving simplified development models are okay for a post-modern everything is allowed world, whilst modernism aims for long-term goals, making it easier for the user, not the developer.
Modernism is based on "Form Follows Function", and not the other way round. Reduce it, abstract it. Functionalism is everything, marketing is less important.
And to avoid popular misconceptions, in our current era "Modern" doesn't mean "New" at all. Modern is more old Stanford-style development. Check the Unix Haters handbook e.g. Rust is new, but this choice alone doesn't allow the use of Modern. Rust is better, because of its superior semantics and guarantees, whilst still adhering to the C ABI. It's a library for everybody afterall, and not comparable to the latest ocaml, haskell or lisp TLS library, which only adheres to their ABI and needs wrappers to be useful for projects in other languages.