void addNestedEnumGroup(EnumGroup enumGroup)
    {
        if (nestedEnumGroups.put(enumGroup.name, enumGroup) != null)
        {
            throw err("Duplicate nested enum: " +
                    enumGroup.name + " from message: " + name, getProto());
        }
    }
Represents the message defined in the {@link Proto}.

@author David Yu
@created Dec 19, 2009
protostuff-parser/src/main/java/io/protostuff/parser/Message.java