XmlIsSet (JAXB OSGI 2.2.11.jbossorg-1 API)

Deprecated.
this hasn't been implemented in the RI, and this hasn't been speced yet. I believe Joe asked for this feature. I'd like to drop this.
```
@Retention(value=RUNTIME)
@Target(value={FIELD,METHOD})
public @interface XmlIsSet
```
Designates a boolean field/property as a flag to indicate whether another property is present or not.
Sometimes you'd want to map a Java primitive type to an optional element/attribute. Doing this makes it impossible to represent the absence of the property, thus you always end up producing the value when you marshal to XML. For example,
```
 XmlElement
 class Foo {
      XmlElement
      int x;
 }

 marshaller.marshal(new Foo());
 
```
and you get:
```
 <foo><x>0</x></foo>
 
```
By creating a side boolean field/property that has this annotation, you can indicate the absence of the property by setting this boolean to false.
```
 XmlElement
 class Foo {
      XmlElement
      int x;
      XmlIsSet("x")
      boolean xIsPresent;
 }

 Foo f = new Foo();
 f.x = 5;
 f.xIsPresent = false;

 marshaller.marshal(f);

 
 <foo/>
 

 f.xIsPresent = true;
 
 <foo><x>5</x></foo>
 
 
```
A property/field annotated with XmlIsSet itself will not show up in XML. It is an error to use this annotation on the same property/field as XmlElement, XmlAttribute, XmlValue, or XmlElementRef, ...TBD.
Author:

Kohsuke Kawaguchi

Required Elements
Modifier and Type	Required Element and Description
`String`	`value` Deprecated. Specifies the name of the property to attach to.

Annotation Type XmlIsSet