protected Extension(char key) 
{
        this.key = key;
}

 Extension(char key,
    String value) 
{
        this.key = key;
        setValue(value);
}

 public String getID() 
{
        return id;
}

 public char getKey() 
{
        return key;
}

 public String getValue() 
{
        return value;
}

 protected  void setValue(String value) 
{
        this.value = value;
        this.id = key + LanguageTag.SEP + value;
}

 public String toString() 
{
        return getID();
}