All Superinterfaces:

java.io.Serializable

All Known Implementing Classes:

LineNumberingNodeFactory.Numbering

Enclosing interface:

Node
```
public static interface Node.HookKey
extends java.io.Serializable
```
Nodes can optional have hooks which add meta-data to the node. This meta-data is identified by a HookKey, typically an enum which implements this interface.
Since Jep 4.0 HookKey extends Serializable. Individual instances can be created as enums:
```
enum EnumKey implements HookKey { KEY1,KEY2 };
```
and get and set using setHook(EnumKey.Key1,3.0) and getHook(EnumKey.Key2). Alternatively anonymous class can be used:
```
 public static final HookKey ANON_KEY = new HookKey() {
           private static final long serialVersionUID = 1L;
           private Object readResolve() { return ANON_KEY; }
 };
 
```
The readResolve() is needed for serialisation.

Interface Node.HookKey