cherry pick #4731 to release-5.0 (#4734)

Signed-off-by: ti-srebot <ti-srebot@pingcap.com>

Co-authored-by: TomShawn <41534398+TomShawn@users.noreply.github.com>

comment-syntax.md

@@ -126,14 +126,14 @@ In TiDB, you can also use another version:
 SELECT STRAIGHT_JOIN col1 FROM table1,table2 WHERE ...
 ```
 
-If the server version number is specified in the comment, for example, `/*!50110 KEY_BLOCK_SIZE=1024 */`, in MySQL it means that the contents in this comment are processed only when the MySQL version is or higher than 5.1.10. But in TiDB, the MySQL version number does not work and all contents in the comment are processed. **Do not leave any space inside the `/*T![` characters**.
+If the server version number is specified in the comment, for example, `/*!50110 KEY_BLOCK_SIZE=1024 */`, in MySQL it means that the contents in this comment are processed only when the MySQL version is or higher than 5.1.10. But in TiDB, the MySQL version number does not work and all contents in the comment are processed.
 
 ## TiDB specific comment syntax
 
 TiDB has its own comment syntax (that is, TiDB specific comment syntax), which can be divided into the following two types:
 
 * `/*T! Specific code */`: This syntax can only be parsed and executed by TiDB, and be ignored in other databases.
-* `/*T![feature_id] Specific code */`: This syntax is used to ensure compatibility between different versions of TiDB. TiDB can parse the SQL fragment in this comment only if it implements the corresponding feature of `feature_id` in the current version. For example, as the `AUTO_RANDOM` feature is introduced in v3.1.1, this version of TiDB can parse `/*T![auto_rand] auto_random */` into `auto_random`. Because the `AUTO_RANDOM` feature is not implemented in v3.0.0, the SQL statement fragment above is ignored.
+* `/*T![feature_id] Specific code */`: This syntax is used to ensure compatibility between different versions of TiDB. TiDB can parse the SQL fragment in this comment only if it implements the corresponding feature of `feature_id` in the current version. For example, as the `AUTO_RANDOM` feature is introduced in v3.1.1, this version of TiDB can parse `/*T![auto_rand] auto_random */` into `auto_random`. Because the `AUTO_RANDOM` feature is not implemented in v3.0.0, the SQL statement fragment above is ignored. **Do not leave any space inside the `/*T![` characters**.
 
 ## Optimizer comment syntax