@Override
    public void putExtraOption(String key, Object value)
    {
        if (extraOptions.put(key, value) != null)
            throw err("Duplicate message option: " + key, 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