On text format: "The textual format is not backwards compatible. We don't change it too often, but there are no specific promises." On C API: "The C API is, in general, a "best effort" for stability. This means that we make every attempt to keep the C API stable, but that stability will be limited by the abstractness of the interface and the stability of the C++ API that it wraps."
There is confusion because C++ API is unstable (very unstable). But C API is stable. And C API is more stable than text format. (In my experience, policy is accurate description of actual practice and not empty promise.)
Ah! I was under the impression that the C API was quasi-deprecated relative to the C++ API, but from what you're saying, it sounds like that's not the case?
On text format: "The textual format is not backwards compatible. We don't change it too often, but there are no specific promises." On C API: "The C API is, in general, a "best effort" for stability. This means that we make every attempt to keep the C API stable, but that stability will be limited by the abstractness of the interface and the stability of the C++ API that it wraps."
There is confusion because C++ API is unstable (very unstable). But C API is stable. And C API is more stable than text format. (In my experience, policy is accurate description of actual practice and not empty promise.)