This interface represents an item in an SVGXXXList.
The item is required to hold a reference to its parent
list so that an item can be moved from one list to another.
A string representation of the item is also required in order
to update the value of the attribute the list containing
the item represents.
If the value of the item is changed, it is required
to notify the list it belongs to in order to synchronized
the list and the attribute the list represents.