All that remains to make the container tree part functional is to complete its settings. Open the settings page for the Container Icon Tree part and enter faceValue for the attributeName property.
Next, select the itemHasChildrenAttributes property in the Name column and ... in the Value column. In the Item Children Accessors window, select the Add push button. A row is added to the table. Enter Card for the Item Class and select hasChildren from the list of the Card part's public attributes in the Has-Children column.
Select OK in the Item Children Accessors window and close the Properties window to accept the changes. Now, whenever the container needs to know whether an item of the Card class has children, it will use its hasChildren get selector to make the determination. The get selector must return a Boolean value.
Save the part.