The type of action for an item update operation. Only use the add action for numbers or sets; the specified value is added to the existing
value. If a set of values is specified, the values are added to the existing set. Adds the specified attribute. If the attribute exists, it
is replaced by the new value. If no value is specified, this removes the attribute and its value. If a set of values is specified, then the
values in the specified set are removed from the old set.
Constraints:

C# |
public string Action { get; set; }