It's up to the developer to place their interfaces in the category they
wish for it to start out in.
+
+
+Notable bits of non-ABI, which should not under any circumstances be considered
+stable:
+
+- Kconfig. Userspace should not rely on the presence or absence of any
+ particular Kconfig symbol, in /proc/config.gz, in the copy of .config
+ commonly installed to /boot, or in any invocation of the kernel build
+ process.
+
+- Kernel-internal symbols. Do not rely on the presence, absence, location, or
+ type of any kernel symbol, either in System.map files or the kernel binary
+ itself. See Documentation/stable_api_nonsense.txt.