Some functions are not exported

The symbols for the functions

struct pw_mempool *pw_mempool_new(struct pw_properties *props);
void pw_mempool_add_listener(struct pw_mempool *pool,
                            struct spa_hook *listener,
                            const struct pw_mempool_events *events,
                            void *data);
void pw_mempool_clear(struct pw_mempool *pool);
void pw_mempool_destroy(struct pw_mempool *pool);
int pw_mempool_remove_id(struct pw_mempool *pool, uint32_t id);
struct pw_loop *pw_data_loop_get_loop(struct pw_data_loop *loop);

are undefined, probably because those functions were not defined with static or SPA_EXPORT.

Is this a bug or a feature?