Analysis of the difference between Max_connections and max_user_connections in Mysql _mysql

In the MySQL manual has a bit of max_user_connections, it is used to restrict user resources, how to restrict user resources? Here's a little test.
The value of the global variable is first produced
Mysql> SELECT @ @max_user_connections;
+------------------------+
| @ @max_user_connections |
+------------------------+
| 0 |
+------------------------+
1 row in Set (0.00 sec)
by default, the system is 0.
What does it mean to be 0? It is said to not restrict user resources.
Here I change the value of it, and in the query, note that this change is not valid after the server reboot, you want to save the words are placed in the options file!
Mysql> SET @ @global. Max_user_connections=1;
Query OK, 0 rows Affected (0.00 sec)
Mysql> SELECT @ @max_user_connections;
+------------------------+
| @ @max_user_connections |
+------------------------+
| 1 |
+------------------------+
1 row in Set (0.00 sec)
now I'm going to reopen a connection.
C:\windows\system32>mysql-uroot-pweb
ERROR 1203 (42000): User Root already has more than ' max_user_connections ' Activ
E connections
This means that the user has reached the maximum number of connections and can no longer connect to own resources!
This parameter can only restrict resources to the whole, cannot restrict a user, if you need to limit a user, you can see in the permission list
max_questions:0
max_updates:0
max_connections:0
max_user_connections:0
These parameters can be restricted to a user.
max_connections means a user limit for the entire server!