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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


Tantek Çelik, Technorati, Inc



This specification is (C) 2003-2023 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.


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


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.


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


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


List Module

 dl, dt, dd, ol, ul, li

Metainformation Module


Stylesheet Module

 style element

Style Attribute Module

 style attribute

Link Module


Legacy Module

 Attribute compact on ol and ul

The XOXO Profile

See XOXO Profile for the XMDP profile of XOXO which defines the XOXO values for the class attribute.

Simple XOXO Fragment


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

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:

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>,