Container Node

A container node is used to group related nodes in a subtree. A container node has only child nodes and no value. A container node may contain any number of child nodes of any type (including the leaf, leaf-list, container, and list nodes).

Containers are classified into existent containers or non-existent containers:

Existent container: The existence of a container is meaningful. For configuration data, a container node provides a configuration button and is also a method of organizing relevant configurations.
Take an existent container node named system as an example. The node contains another container node named services. YANG example:
```
container system {
 container services{  
   container ssh{
  presence "Enables SSH";     
    // more leafs, containers and stuff here... 
  }
 }
}
```
NETCONF XML example:
```
<system>
 <services>
  <ssh/>
 </services>
</system>
```
Non-existent container: A container itself is meaningless. It functions as a hierarchy for organizing data nodes and accommodating child nodes. By default, a container is in the format of non-existent container.
Take a non-existent container node named system as an example. The node contains another container node named login, which contains a leaf node named message. YANG example:
```
container system {
 container login {
  leaf message {
   type string;
   description
   "Message given at start of login session";
  }
 }
}
```
NETCONF XML example:
```
<system>
 <login>
  <message>Good morning</message>
 </login>
</system>
```