RSS enclosure

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 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.

Syntax

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>.

Similar technologies

The RSS &lt;enclosure&gt; has similarities to:

• the SMIL &lt;prefetch&gt; element,
• the HTML......
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