539a7e1a_RSS_Field_Descriptions__Required___Optional
[Name of Field] Enclosure [Description of Feed] Information about a file that is to be included with the item. URL The URL for the file. Length The length of the file (in bytes). Type The MIME type of the file. [Required / Optional] 
Including an Enclosure with your feed is optional. However, if you enter information is any Enclosure field, then you must enter proper information into all the Enclosure fields.
RSS Field Descriptions
Required / Optional