Document attribute defaults are the result of all of the processes already described and are effectively the baseline for attributes' default values once a document is created. System attribute defaults are documented. New user attributes take their data-type defaults.
The document is the highest possible level for configuration of User attributes, as they only exist in a document if added by the user.
Document defaults can always be reviewed—or indeed altered, where allowed—using the Document Inspector's System and User tabs.
Next, the role of prototypes…
See also—notes linking to here: