public boolean isValueCompatible(Annotation structValue) {
        if (structValue.getType().inherits(this)) {
            //the value is of this type; or the supertype of the value is of this type, etc....
            return true;
        }
        return false;
    }
Returns the ID of this annotation.
document/src/main/java/com/yahoo/document/annotation/AnnotationType.java