Many parts of Linux kernel is still undocumented too. But still people have such great confidence in its consistency. One example is sys_brk / sbrk. It is not explicitly stated in the man whether it will be aligned to a page boundary or not, but it is. Now should we re-align the returned pointer to some aligned address just because it's not documented or we are applying 'defensive programming'?

or if you know that you can update your code also when in the future something changes.

Now you're accusing Linux future changes are not backward-compatible as well!

Do you hate Linux that much? :p