The annotation XmlSeeAlso instructs JAXB to include the specified classes in the set of recognized classes, i.e., the ones that are bound to schema elements. The typical case where this is required is for the subclasses of some class that is included, in contrast to those classes that are statically referenced, e.g., becauae they are used as types for a field. You use XmlSeeAlso on some class, as shown in the example below:

@XmlSeeAlso( {Dog.class, Cat.class} )
class Animal {
   //...
}