Specify the attributes of keychain items.
In addition to the data that you want to store, keychain items also have attributes that allow you to find them later and that allow you to control how the data is used or shared.
You specify attributes as the keys and values of a dictionary. The available attribute keys are listed below. Typically, the corresponding value is a string, a number, or some other basic type, as given in each key description. In a few cases, the value comes instead from a list of a known constants. These predefined attribute values are also listed below, grouped according to the key that they serve.