MDL-37761 Backup: Add phpdoc for MODE constants

backup/backup.class.php

@@ -51,8 +51,25 @@ abstract class backup implements checksumable {
 
     // Predefined modes (purposes) of the backup
     const MODE_GENERAL   = 10;
+
+    /**
+     * This is used for importing courses, and for duplicating activities.
+     *
+     * This mode will ensure that files are not included in the backup generation, and
+     * during a restore they are copied from the existing file record.
+     */
     const MODE_IMPORT    = 20;
     const MODE_HUB       = 30;
+
+    /**
+     * This mode is intended for duplicating courses and cases where the backup target is
+     * within the same site.
+     *
+     * This mode will ensure that files are not included in the backup generation, and
+     * during a restore they are copied from the existing file record.
+     *
+     * For creating a backup for archival purposes or greater longevity, use MODE_GENERAL.
+     */
     const MODE_SAMESITE  = 40;
     const MODE_AUTOMATED = 50;
     const MODE_CONVERTED = 60;