Standards are nice and dandy, real-world-implementations all suffer from bugs, missing features or implement undefined behavior slightly different. So if you wa

Standards are nice and dandy, real-world-implementations all suffer from bugs, missing features or implement undefined behavior slightly different. So if you want to support an implementation, you need to test it. If there multiple versions of an implementation you want to support, you need to test them all. Any other approach is "it works on X, it might work on Y, but we're not actively supporting Y."