> A classic example would be whether an API that munges filesystem paths should resolve symlinks or not -- if this is unspecified, then changing that behaviour

> A classic example would be whether an API that munges filesystem paths should resolve symlinks or not -- if this is unspecified, then changing that behaviour is technically not a breaking change Another example would be Ruby 2.4 changing String#upcase & friends from handling ASCII only to being unicode aware with a new argument to override and changing the default. Technically a breaking change but actually silently fixes a ton of bugs.