@Override
            public String messageName()
            {
                return Array.class.getSimpleName();
            }
This base class handles all the IO for reading and writing polymorphic fields. When a field's type is
polymorphic/dynamic (e.g interface/abstract/object), the type (id) needs to be written (ahead) before its
value/content to be able to deserialize it correctly.
<p>
The underlying impl will determine how the type (id) should be written.
<p>
An {@link IdStrategy} is standalone if the {@link #primaryGroup} is not set.

@author Leo Romanoff
@author David Yu
protostuff-runtime/src/main/java/io/protostuff/runtime/IdStrategy.java