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 aggregator
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
, arguably 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.
In RSS 2.0, the syntax for the <enclosure> tag, an optional child of the <item> element, is as follows:
<source lang="xml"><enclosure url="http://example.com/file.mp3" length="123456789" type="audio/mpeg" /></source>
where the value of the url
attribute is a URL
of a file, length
is its size in bytes
, and type
its mime type
There may only be a single <enclosure> per <item>.
The RSS <enclosure> has similarities to:
- the SMIL <prefetch> element,
- the HTML......