client API: explain when mpv_create() can return NULL

libmpv/client.h

@@ -403,7 +403,10 @@ const char *mpv_client_name(mpv_handle *ctx);
  * client handle. (Whether concurrent access is definitely allowed or not has
  * yet to be decided.)
  *
- * @return a new mpv client API handle
+ * @return a new mpv client API handle. Returns NULL on error. Currently, this
+ *         can happen in the following situations:
+ *         - out of memory
+ *         - LC_NUMERIC is not set to "C" (see general remarks)
  */
 mpv_handle *mpv_create(void);