The reason for the new annotation syntax is the annotations are much richer in their details than merely stating when an object is freed by a function. They can express subtle preconditions, such as the expectation that a pointer refer to a region that is heap-allocated, or be a valid lvalue or rvalue, and so on, and also capture more general side effects.

As per the issue of backward-compatibility, Xr0 strips the annotations with a simple command: `0v -s`, producing C source that works with C compilers.