This module allows site administrators to add additional HTML attributes to the wrapping markup on any field in the Manage Display settings page.
The field formatter attributes settings are found in the Manage display tab for content types, users, and other entities. A options element is available for each field formatter, revealed by using the formatter settings edit button (Gear wheel icon) for that field.
Why use this module?
This module is good if - for example - you need a quick & dirty way of adding schema.org microdata attributes to fields. A better solution to this problem is found in the Microdata module, but most field formatters are not yet supported. *edit: An even better solution to this problem is the Schema.org module which, while not technically supporting the recommended microdata format on schema.org, uses RDFa 1.0 which all the search engines support nicely.