xoxo

XOXO 1.0: Extensible Open XHTML Outlines

XOXO is a simple, open outline format written in standard XHTML and suitable for embedding in (X)HTML, Atom, RSS, and arbitrary XML. XOXO is one of several microformat open standards.

Draft Specification 2004-10-01

Editor

Tantek Çelik, Technorati, Inc

Authors

• Kevin Marks, Technorati, Inc
• Tantek Çelik, Technorati, Inc (formerly of Microsoft Corporation)
• Mark Pilgrim, IBM
• Morten W. Petersen

Copyright

This specification is (C) 2003-2024 by the authors. However, the authors intend to submit (or already have submitted, see details in the spec) this specification to a standards body with a liberal copyright/licensing policy such as the GMPG, IETF, and/or W3C. Anyone wishing to contribute should read their copyright principles, policies and licenses (e.g. the GMPG Principles) and agree to them, including licensing of all contributions under all required licenses (e.g. CC-by 1.0 and later), before contributing.

Patents

This specification is subject to a royalty free patent policy, e.g. per the W3C Patent Policy, and IETF RFC3667 & RFC3668.

Preamble

When we were discussing Attention.xml, Tantek pointed out that XHTML has everything necessary for semantically expressing outlines and blogroll-like subscriptions in an XML format that is both interactively renderable by browsers and parsable by strict XML engines. This page is here to discuss this idea.

Name

XOXO stands for eXtensible Open XHTML Outlines, and is pronounced variously as 'ecks oh ecks oh', 'zho-zho', or 'sho-sho'.

Abstract

XOXO is one of several MicroFormats. This specification defines a new XHTML document type that is based upon the module framework and modules defined in Modularization of XHTML (XHTMLMOD). The purpose of the XOXO document type is to serve as the basis for XHTML friendly outlines for processing by XML engines and for easy interactive rendering by browsers.

The XOXO Document Type

The XOXO document type is made up of the following XHTML modules. The elements, attributes, and minimal content models associated with these modules are defined in "Modularization of XHTML" (XHTMLMOD). The elements are listed here for information purposes, but the definitions in "Modularization of XHTML" should be considered definitive. In the on-line version of this document, the module names in the list below link into the definitions of the modules within the current version of "Modularization of XHTML".

Structure Module

 body, head, html, title

Hypertext Module

 a

List Module

 dl, dt, dd, ol, ul, li

Metainformation Module

 meta

Stylesheet Module

 style element

Style Attribute Module

 style attribute

Link Module

 link

Legacy Module

 Attribute compact on ol and ul

The XOXO Profile

The XOXO Profile is an XHTML Meta Data Profile used to define values for the class attribute.

<dl class="profile">
 <dt>class</dt>
 <dd><p><a rel="help" href="http://www.w3.org/TR/html401/struct/global.html#adef-class">
 HTML4 definition of the 'class' attribute.</a>  
  This meta data profile defines some 'class' attribute values 
  (class names) and their meanings as suggested by a 
  <a href="http://www.w3.org/TR/WD-htmllink-970328#profile">draft of "Hypertext
   Links in HTML"</a>:</p>
     <dl>
     <dt>xoxo</dt>
        <dd>An XOXO outline as defined by the 
         <a href="http://microformats.org/wiki/XOXO">XOXO
          specification</a>.  
         Typically an ordered list <ol> or unordered list <ul>
          element.</dd>
     <dt>blogroll</dt>
        <dd>When used with the aforementioned 'xoxo' value, this value means 
         a particular instance of an XOXO outline which has the additional
          semantic of being a 
         <a href="http://www.microcontentnews.com/resources/glossary/blogrolling.htm">blogroll</a>.
        </dd>
     </dl>
 </dd>
</dl>

Simple XOXO Fragment

Markup

<ol class='xoxo'>
  <li>Subject 1
    <ol>
        <li>subpoint a</li>
        <li>subpoint b</li>
    </ol>
  </li>
  <li>Subject 2
    <ol compact="compact">
        <li>subpoint c</li>
        <li>subpoint d</li>
    </ol>
  </li>
  <li>Subject 3
    <ol>
        <li>subpoint e</li>
    </ol>
  </li>
</ol>

Sample Rendering

   1. Subject 1
      a. subpoint a
      b. subpoint b
   2. Subject 2
   3. Subject 3
      a. subpoint e

Usage of 'compact' attribute

Note the use of the 'compact' attribute to indicate that the subpoints of the headline "Subject 2" are not in an expanded state. The absence of the 'compact' attribute elsewhere indicates that the other headlines are in an expanded state.

Possible Default Style Rules for Sample Rendering

ol.xoxo { list-style:decimal; }
ol.xoxo ol { list-style:lower-latin; }
ol[compact="compact"] { display:none; }

More Simple Examples

MarkP has a set of examples that demonstrates both the simplicity of the markup and the presentational richness that is possible:

• simple XO file that can be embedded directly into an XHTML page
• XO with nested groups, also directly embeddedable in XHTML
• XO as a standalone XHTML page (valid XHTML)
• XO as a standalone XHTML page, styled with CSS (also valid XHTML)
• Chris Holland Outline Helper: tweaked one of above samples, yanked CSS for simplicity, added reference to outlines.css and outlines.js, pasted a few different combinations of ul/ol/li with the compact attribute.
  • in trying to comply with semantic principles the "compact" attribute to ol and ul elements is what drives the display state. Via scripting, i'm setting classes on containing li element for added styling flexibility, though CSS Gurus might be able to replace "li.expanded" in outlines.css with some other CSS selector that says "select an li node that contains an ol node with a 'compact' attribute set".

Properties of Outline Items

Outlines typically consist of a hierarchy of points and subpoints. Each of those points (outline items) itself may have some properties (AKA attributes or metadata) that need to be represented. Perhaps the most common additional property on outline items in practice is the URL as demonstrated in Mark Pilgrim's examples above. Even the text label/title of an outline item could be considered a common property. A few such common properties:

• text
• description
• url (often called xmlurl or htmlurl; sometimes called permalink)
• title
• type (hint of the MIME type of the resource indicated by the URL)

In general, properties on an outline item <li> are represented by a nested definition list <dl>. Strictly speaking, it is the first <dl> inside the <li> and before any following <ol>, <ul>, or <li>, e.g. here is an item "item 1" with a description property (the subpoints are there purely as a point of reference to an earlier example).

<ol class='xoxo'>
  <li>item 1
    <dl>
      <dt>description</dt>
        <dd>This item represents the main point we're trying to make.</dd>
    </dl>
    <ol>
      <li>subpoint a</li>
      <li>subpoint b</li>
    </ol>
  </li>

Special Properties

There are a handful of special properties which we are able to represent more directly and conveniently with the semantic XHTML building blocks that we have included, instead of terms in a definition list. Mostly taken from the above list of common properties, these are:

• text, url, title, type, and rel (short for relationship)

If we were to represent them simply as definition terms (including the "description" property from the previous example), they might look something like this:

Example for the sake of discussion only / not a canonical XOXO example:

<ol class='xoxo'>
  <li>
    <dl>
      <dt>text</dt>
        <dd>item 1</dd>
      <dt>description</dt>
        <dd> This item represents the main point we're trying to make.</dd>
      <dt>url</dt>
        <dd>http://example.com/more.xoxo</dd>
      <dt>title</dt>
        <dd>title of item 1</dd>
      <dt>type</dt>
        <dd>text/xml</dd>
      <dt>rel</dt>
        <dd>help</dd>
    </dl>
  </li>

However, by taking advantage of the semantic <a href> element, we are able to dramatically simplify the common cases that utilize these properties. From a parser's perspective, this applies to the first <a href> element directly inside the <li>.

Actual XOXO Example:

<ol class='xoxo'>
  <li><a href="http://example.com/more.xoxo"
         title="title of item 1"
         type="text/xml"
         rel="help">item 1</a> 
<!-- note how the "text" property is simply the contents of the <a> element -->
      <dl>
        <dt>description</dt>
          <dd>This item represents the main point we're trying to make.</dd>
      </dl>
  </li>

Any other properties are simply added to the definition list in the same way as the "description" property.

XOXO Schemas

This section is informative.

Note: these may be out of date and require updating to reflect the use of <dl> for annotating XOXO items with arbitrary properties.

• DTDs
• Schemas (Relax NG and DTDs)

Examples in the Wild

This section is informative.

Too numerous to document thoroughly. Nearly every blogroll on the Web can be parsed as XOXO, since they are typically an unordered list of list items of hyperlinks, which is within the XOXO profile.

Sample Code

This section is informative.

• See the xoxo-sample-code page for open source sample code to read and write XOXO files.

Implementations

This section is informative.

• Les Orchard has written a nice XOXO outline editor in javascript.
• http://homepage.mac.com/ctholland/thelab/outlines/ is a great demonstration of dynamic interactive XOXO with use of "compact" and DHTML to collapse/expand.
• http://tool-man.org/examples/sorting.html is a great demonstration of drag and drop sortable XOXO lists with javascript and CSS.
• http://www.joshpeek.com/projects/opmltoxoxois an extensible OPML to XOXO converter.
• http://www.opendarwin.org/~drernie/xoxo-datatypes.html Mapping XOXO to Mac OS X property lists
• single line of rails to convert XOXO to HTML

References

Normative References

• XHTML 1.0
• XHTMLMOD
• XMDP
• XFN

Informative References

This section is informative.

• Attention.xml
• VoteLinks
• XHTML 1.1
• OPML 1.0
• Contributed from http://developers.technorati.com/wiki/XOXO

Related Read

• Patrick Logan on why OPML and a Microsoft Lists extension are both unnecessary.

Similar Work

• XHTML Outlines - DannyAyers independently came up with idea in 2003 October (just a month or two before Kevin and Tantek independently came up with XOXO) to use a simple profile of XHTML to semantically represent outlines using existing building blocks from XHTML.
• XOW - making them editable, producing RDF and bookmark lists from them (DannyAyers)

Discussions

This specification is a work in progress. As additional aspects are discussed, understood, and written, they will be added. There is a separate document where we are keeping our brainstorms and other explorations relating to XOXO:

• See also blogs discussing this page.

Q&A

• If you have any questions about XOXO, check the xoxo-faq, and if you don't find answers, add your questions!

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Issues

• Please add any issues with the specification to the separate xoxo-issues document.