OPML


OPML is an XML format for outlines. Originally developed by UserLand as a native file format for the outliner application in its Radio UserLand product, it has since been adopted for other uses, the most common being to exchange lists of web feeds between web feed aggregators.
The OPML specification defines an outline as a hierarchical, ordered list of arbitrary elements. The specification is fairly open which makes it suitable for many types of list data.
Support for importing and exporting RSS feed lists in OPML format is available in Mozilla Thunderbird, and many other RSS reader web sites and applications.

XML format

The XML elements in an OPML document are:
; <opml version="1.0">
; <head>
; <body>
; <outline>

Criticism

  1. The RFC 822 date format is considered obsolete, and amongst other things permits the representation of years as two digits. In general, date and time formats should be represented according to RFC 3339.
  2. Due to the semantics of the "expansionState" attribute:
  3. * The expansion state of the children of collapsed nodes cannot be stored
  4. * When an outline element is expanded, collapsed, added, deleted or moved, the expansion state of all elements below it must be recalculated
  5. Due to the arbitrary nature of the "type" attribute, and the acceptance of arbitrary attributes on "outline" elements, interoperability of OPML documents relies almost entirely on the undocumented conventions of content producers.
  6. MIME types aren't clear; text/xml usually merely identifies the document as having XML content, while text/x-opml does not specify that the document is XML since it lacks the +xml suffix.

    Validation

has made a request for comments on a and released a beta .
Katy Ginger from DLESE has published for validating OPML 2.0. There is also a .

Alternative specifications

Alternative specifications have been proposed, notably these include OML, XOXO and XBEL.