* This number should be one less than the total number of parts in the
* split WIM. Set to 0 if the WIM is a standalone WIM.
* @param staging_dir
- * Currently ignored, but may provide a way to specify the staging
- * directory in the future. Set to @c NULL.
+ * If non-NULL, the name of a directory in which the staging directory will
+ * be created. Ignored if ::WIMLIB_MOUNT_FLAG_READWRITE is not specified
+ * in @a mount_flags. If left @c NULL, the staging directory is created in
+ * the same directory as the WIM file that @a wim was originally read from.
*
* @return 0 on success; nonzero on error.
* @retval ::WIMLIB_ERR_ALREADY_LOCKED