One approach to guard against Hyrum’s Law is GREASE (aka “Generate Random Extensions And Sustain Extensibility” used in the TLS 1.3 protocol) i.e. behavior randomization to avoid inadvertent dependencies on unspecified behavior: https://textslashplain.com/2020/05/18/a-bit-of-grease-keeps-... What are other approaches?
When people don't know which implementation will be used, they tend to stick to the standard or the documentation.
We see this in places like the C language or in Common Lisp. Library writers must take into account that the implementation they use their library on may not be the same as the implementation their users will use.