in
MySQL-5.7 that are not ported to MariaDB 10.x yet.

/*!50701 MariaDB-10.x ignores MySQL-5.7 specific code */

Note: comments which have a version number in the range 50700..99999 that use
MariaDB-style executable comment syntax are still executed.

/*M!50701 MariaDB-10.x does not ignore this */

Statement delimiters cannot be used within executable comments.

Examples
--------

In MySQL all the following will return 2: In MariaDB, the last 2 queries would
return 3.

SELECT 2 /* +1 */;
SELECT 1 /*! +1 */;
SELECT 1 /*!50101 +1 */;
SELECT 2 /*M! +1 */;
SELECT 2 /*M!50301 +1 */;

The following executable statement will not work due to the delimiter inside
the executable portion:

/*M!100100 select 1 ; */
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual
that corresponds to your MariaDB server version for the right syntax to use
near '' at line 1

Instead, the delimiter should be placed outside the executable portion:

/*M!100100 select 1 */;
+---+
| 1 |
+---+
| 1 |
+---+

URL: https://mariadb.com/kb/en/comment-syntax/https://mariadb.com/kb/en/comment-syntax/