RSS enclosures are a way of attaching multimedia content to RSS feeds by providing the URL of a file associated with an entry, such as an MP3 file to a music recommendation or a photo to a diary entry. Unlike e-mail attachments, enclosures are merely hyperlinks to files. The actual file data is not embedded into the feed (unless a data URL is used). Support and implementation among aggregators varies: if the software understands the specified file format, it may automatically download and display the content, otherwise provide a link to it or silently ignore it. The addition of enclosures to RSS, as first implemented by Dave Winer in late 2000 , was an important prerequisite for the emergence of podcasting, perhaps the most common use of the feature . In podcasts and related technologies enclosures are not merely attachments to entries, but provide the main content of a feed. Syntax In RSS 2.0, the syntax for the <enclosure> tag, an optional child of the <item> element, is as follows: <enclosure url="http://example.com/file.mp3" length="123456789" type="audio/mpeg" /> where the value of the url attribute is a URL of a file, length is its size in bytes, and type its mime type. It is recommended that only one <enclosure> element is included per <item>. Prefetching The RSS <enclosure> has similarities to: the SMIL <prefetch> element, the HTML <link> element with rel="prefetch". the HTTP Link header with rel="prefetch". (See section 19.6.2.4.) the Atom <link> element with rel="enclosure" See also Broadcatching Internet television Podcast Photofeed Vlog References External links The <enclosure> tag in the RSS 2.0 specification mod_enclosure - Enclosures in RSS 1.x RSS Web syndication formats XML-based standards