Creates an item for the given label and value and appends it to the
container.
| aLabel | - the label for the new item |
| aValue | - the value of the new item |
Creates an item for the given label and value and inserts it into the
container at the specified position.
| aIndex | - the index where the new item will be inserted |
| aLabel | - the label for the new item |
| aValue | - the value of the new item |
Removes an item from the container.
| aIndex | - index of the item to remove |
Returns the index of an item or -1 if the item is not in the container.
| aItem | - the item to determine the index of |
Returns the item at a given index or null if the item is not is the
container.
| aIndex | - the index of the item to return |
Returns a count of items in the container.