+ * details on how this mode works.
+ *
+ * Additional notes: @a sources is not a @c const parameter and you cannot
+ * assume that its contents are valid after this function returns. You must
+ * save pointers to the strings in these structures if you need to free them
+ * later, and/or save copies if needed.
+ *
+ * It is also possible for this function to return ::WIMLIB_ERR_INVALID_OVERLAY
+ * when trying to overlay a non-directory on a directory or when otherwise
+ * trying to overlay multiple conflicting files to the same location in the WIM
+ * image. */