+/**@{
+ * Schema compatibility flags.
+ *
+ * Used as flags in a bit field that indicates whether the old or new schema (or both)
+ * are read or written.
+ *
+ * - SCHEMA_COMPAT_WRITE_OLD: Whether information is written to the old schema.
+ * - SCHEMA_COMPAT_READ_OLD: Whether information stored in the old schema is read.
+ * - SCHEMA_COMPAT_WRITE_NEW: Whether information is written to the new schema.
+ * - SCHEMA_COMPAT_READ_NEW: Whether information stored in the new schema is read.
+ */
+define( 'SCHEMA_COMPAT_WRITE_OLD', 0x01 );
+define( 'SCHEMA_COMPAT_READ_OLD', 0x02 );
+define( 'SCHEMA_COMPAT_WRITE_NEW', 0x10 );
+define( 'SCHEMA_COMPAT_READ_NEW', 0x20 );
+define( 'SCHEMA_COMPAT_WRITE_BOTH', SCHEMA_COMPAT_WRITE_OLD | SCHEMA_COMPAT_WRITE_NEW );
+define( 'SCHEMA_COMPAT_READ_BOTH', SCHEMA_COMPAT_READ_OLD | SCHEMA_COMPAT_READ_NEW );
+define( 'SCHEMA_COMPAT_OLD', SCHEMA_COMPAT_WRITE_OLD | SCHEMA_COMPAT_READ_OLD );
+define( 'SCHEMA_COMPAT_NEW', SCHEMA_COMPAT_WRITE_NEW | SCHEMA_COMPAT_READ_NEW );
+/**@}*/
+