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This page is used to document any issues in XSLT that converts XOXO to OPML, any short comings that need to be addressed in XOXO that are REQUIRED in OPML, and any issues with News Readers when they import OPML files that have been generated from XOXO. The original request was to the mailing list on September 25th


Draft conversion principles

OPML specifies limitations in a loose way, using the type attribute. There is some formal canonicalisation (in the 1.0 spec and the 2.0 spec) of what individual type attributes do. Type attribute values extend the standard attribute set of the outline node. So, for instance, the "rss" type value tells the processor to look for feed-specific values.

MIME type

OPML is usually served with a large variety of MIME types including:

There have been suggestions as to whether or not to start serving OPML as:

One should not infer that something is or is not OPML based on the MIME type, because that's not reliable. But all OPML-to-XOXO tools ought to point to OPML files (includes, etc.) in a consistent way. That way, JavaScript could be laid over the top of XOXO outlines to allow them to include OPML outlines or link to them in a way that would proxy them back in to XOXO (etc.).

Text attribute

There is some confusion over the difference between the text and title attributes. Both are reasonably well-defined by the OPML specification, and serve different purposes. Some implementations of OPML break from the specification in providing a title attribute but not a text attribute. If a text attribute is present but not a title attribute, one should infer that the text attribute is equal to the title attribute. One should not infer that the title attribute is equivalent to the text attribute (see OPML 2.0 Spec).

The text attribute can and does often contain escaped HTML markup (which is really a bad practice, and has led to a lot of criticism of OPML). This is standard behavior from the OPML Editor. An OPML-to-XOXO parser should ideally take data from the text attribute and put it into a XOXO outline in a standard way.

Known type attribute values


A blank type attribute usually implies that it is a text node in an outline, using the text and created nodes. This is usually the behavior of most outliners and is the default behavior of the OPML Editor.

RSS Feed

The type attribute is set to string rss, implies following attributes:

What should be done with an RSS feed node? Since it is almost the primary use of OPML, it would probably be advisable to optimize any conversion effort to deal efficiently with feeds.

The text attribute may list something different from the title of the linked feed, so that ought to be the value of the hyperlink - one may link to the blog "Epeus' Epigone" and set the text field as "Kevin Marks".

If the version attribute is present, it should be used to drop in the relevant MIME-type on the link to the feed.

Ideally, an OPML-to-XOXO converter would also locate the HTML versions of feeds if the htmlUrl attribute is not there, and vice versa.

Another implementation note for the version attribute: it's a good idea to check for both upper and lower case versions (eg. the standard "RSS" and the lower-case "rss"). Although the values are enumerated in the specification, I'm betting there are probably misuses out there.


The type attribute in OPML 2.0 is set to include. Otherwise, the include mode is inferred if the type is set to link and the url attribute ends in ".opml".

Ideally, if the include mode is triggered, the HTML should represent it as a hyperlink to the OPML document, perhaps as follows:

<li><a href="[url]" type="application/xml+opml">[text]</a></li>

Date-time stamp

OPML contains a "created" time-stamp, which is generally used in outliners but not in feed readers. The created attribute uses RFC 822 date format. The datetime-design-pattern could be used to represent it, perhaps with a classname of created.

Mapping proprietary extensions

OPML is extensible through the use of namespaced elements and attributes.

There are some proprietary extensions which it would not be appropriate to map to XOXO. The GrazrScript extension is probably one of those. There is no value in mapping it to XOXO, as it will not serve any purpose. Converters should ignore it.

Currently, the following proprietary/non-canonical extensions to OPML can be mapped to XOXO:

Preliminary Mapping

Currently, I am trying to work on a preliminary mapping from OPML and the internal Frontier outline format (on which OPML is strongly based on, and with which it is compatible. This is unreleased so far, but I put the mappings up so that people can suggest improvements to the semantics.

Each of the 'li' elements can, of course, use the compact attribute.

The text type:


The feed type:

<li><a href="[@htmlUrl]" class="feed">[text()]</a> <a href="[@xmlUrl]" class="feed-xml" type="application/xml">RSS</a></li>

(The text label "RSS" can, of course, be changed to 'feed' or 'Atom' or any other text label that you wish. The 'feed' class is to enable reverse XOXO-to-OPML)

The include type:

<li><a href="[@include]" class="opml-include" type="[MIME]">[text()]</a></li>

Test Cases

I have started maintaining a list of OPML Test Cases and Tools for work on OPML-XOXO work. I have also put up an unofficial test suite and schema. --TomMorris 16:48, 7 Mar 2008 (PST)



XSLT Issues

Currently the output from the XOXO to OPML web service does not validate against the BETA OPML validator at [3] the errors/warnings are vauge and are not really issues because the files are still correctly imported into Several Applications

I have no idea if there is an Enumerated List of possible TYPE values in OPML, at the moment i am using the TYPE attribute in HTML and that is MimeType.

New Readers

Please follow the format and add any issues with your News Reader




See also

xoxo-opml-issues was last modified: Wednesday, July 23rd, 2014