include-pattern

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Include Pattern

The include pattern is a microformat design pattern, providing a mechanism to include a portion of data from one area of a page into another area of the same page, allowing the data to be reused by multiple microformats, independent of content order, without repeating all the information. The following is documentation for re-use of the pattern in other microformats, and for publishers working with it.

Editors
Tantek Celik
Ben Ward

background

hResume needed the ability to include a name from one hCard at the top of a resume — the person's contact details — into the separate hCards used in the same person's employment history. Repeating name information would not have matched the existing publishing practices used in Resumes and Curriculum Vit?, would be inconvenient to publishers, and irritating to consumers. The include pattern is a mechanism to reference data from the same page, avoiding repetition, or duplicate visible information.

scope

The include pattern is strictly limited to the scope of the current page. It cannot be used to include content from other URLs.

quick reference

The include-pattern is a mechanism to include content from one microformat into another microformat elsewhere in the same document, using hyperlinks or object. For example: 

<a class="include" href="#author">James Levine</a>

<object class="include" data="#author"></object>

In specifications which cite the include-pattern, either of the above code snippets MUST cause a microformats parser to replace the A or object element with class name "include" with the content fragment with ID "author". Full examples follow.

in general

To reference includes, use an include element with class name "include" and a document fragment identifier. The content to be included should have an ID attribute set, and that ID should be referenced from the HREF or DATA attribute at the point of inclusion.

The include element with class name "include" indicates a reference to a sub-tree elsewhere in the document which MUST be included in-place by microformat parsers. That is, the element with class "include" is _replaced_ in the DOM by the referenced sub-tree. Note that this means all other class names on the include element are discarded. Microformat class names should be included on the target of the include, not on the include element itself.

To prevent infinite loops, if a class="include" refers to itself or to an ancestor in the parse tree, then it is ignored and has no effect on the parser.

Per the scope, the object 'data' attribute and hyperlink 'href' attribute MUST be local ID references when used as include pattern instances. External references (requiring a consuming application to load an external resource) are not supported by this method.

There are two HTML elements available to reference includes, hyperlink/Anchor and object. They are documented below.

These methods of property indirection via a hyperlink element can apply to any/all properties in class-based microformats, but should only be used where a microformat explicitly states that the include-pattern is a dependency. For example, XOXO does not reference the include-pattern at this time, so sub-trees cannot be included by reference in XOXO. hResume and hReview do reference the include pattern.

Hyperlink

The recommended way to reference includes within microformats is to use a hyperlink.

Hyperlink example

Here is an hCard for a bar, included at the top of a reviews page, shown here as a verbose hCard. 

<div class="vcard" id="bricklayers-card">
  <div class="fn org">The Bricklayers Arms</div>
  <div class="adr">
     <span class="street-address">31 Gresse Street</span>,
     <span class="locality">Fitzrovia</span>
     <span class="region">London</span>
     <span class="postal-code">W1T 1QS</span>
  </div>
</div>

Elsewhere on the page, a number of reviews reference the hcard in the item property. Rather than repeat all the verbose detail, only the name is reprinted and the detailed hcard referenced using the include-pattern. 

<div class="hreview">
   <h1 class="summary">A great venue for monthly gatherings!</h1>
   <div class="item"><a class="include" href="#bricklayers-card">The Bricklayers Arms</a></div>
   <p class="description">Wonderful pub, cheap beer, open fire to warm mince pies at Christmas.</p>
</div>

<div class="hreview">
   <h1 class="summary">Takes a while to thin out, but!</h1>
   <div class="item"><a class="include" href="#bricklayers-card">The Bricklayers Arms</a></div>
   <p class="rating"><span class="value">5</span>/<span class="best">5</span></p>
</div>

Note that you MUST include content within the anchor element. See the notes and issues below.

A microformat parser MUST treat each review as follows, with the hyperlink include element completely replaced (including inner-text) by the sub-tree that was referenced: 

<div class="hreview">
   <h1 class="summary">A great venue for monthly gatherings!</h1>
   <div class="item">
      <div class="vcard" id="bricklayers-card">
        <div class="fn org">The Bricklayers Arms</div>
        <div class="adr">
           <span class="street-address">31 Gresse Street</span>,
           <span class="locality">Fitzrovia</span>
           <span class="region">London</span>
           <span class="postal-code">W1T 1QS</span>
        </div>
      </div>
   </div>
   <p class="description">Wonderful pub, cheap beer, open fire to warm mince pies at Christmas.</p>
</div>

notes and issues

Note: The id attribute value in the example "bricklayers-card" was chosen for demonstration purposes. The text of the value has no semantic per the include-pattern other than to connect the source of the include to the destination. Authors SHOULD use good POSH techniques to choose id and class names.

Authors MUST supply content text for the hyperlink itself. This can require repeating a small piece of information (such as a person's name in an hcard), or including generic text as appropriate to the context of the page.

accessibility
  • Testing indicates that the only way to guarantee accessibility of hyperlinks to users of assistive technology (such as screen readers) is to include inner-text. See: Empty Links and Screen Readers
  • You MUST include inner-text in the hyperlink element.
  • You MAY enhance the rendered user experience (depending on the context of your page) by hiding the include element using CSS display: none
  • Where you wish to hide the content of the include element, you SHOULD NOT hide the include element using a CSS negative margin offset as the hidden link will remain in the tab order of the document. Use display: none instead.

Where a publishing constraint prevents putting content within the include-pattern, you MUST use the object element pattern instead of a hyperlink.

Object

The Object Include Pattern is semantically superior to the Hyperlink Include; it is being used to embed content into the page. The object element based include was the original developed include pattern. However, there are some browser compatibility issues that can affect some implementation scenarios and thus the above Hyperlink Include Pattern is preferred.

Object example

The hCard from the beginning of a resume describes the person who's resume it is: 

<span class="vcard">
  <span class="fn n" id="james-hcard-name">
    <span class="given-name">James</span> <span class="family-name">Levine</span>
  </span>
</span>

Elsewhere on the page, a second hCard, with employer information, re-uses the "fn n" content from the first hCard: 

<span class="vcard">
 <object class="include" data="#james-hcard-name"></object>
 <span class="org">SimplyHired</span>
 <span class="title">Microformat Brainstormer</span>
</span>

A microformat parser MUST treat the second hCard as follows, with the object include element completely replaced by the sub-tree that it referenced: 

<span class="vcard">
  <span class="fn n" id="james-hcard-name">
    <span class="given-name">James</span> <span class="family-name">Levine</span>
  </span>
  <span class="org">SimplyHired</span>
  <span class="title">Microformat Brainstormer</span>
</span>

This method of hCard property indirection via an object element can apply to any/all properties in class-based microformats.

notes and issues

  • Unlike the hyperlink pattern, the object is not believed to cause problems in assistive technology when fallback text is absent. (research needed)
  • Apple's Safari 1.x browser has some rendering issues with this use of object: Publishers SHOULD style a width and height of "0" for the include elements to resolve this (clarification of issue needed).
  • Bugs have been reported in some web browsers (Internet Explorer, Safari, Firefox) that object elements referencing fragments of the same document erroneously cause the browser to make additional HTTP requests (version(s) affected needed). For scenarios where HTTP requests are a performance issue, publishers SHOULD use the hyperlink pattern instead.
  • Versions of Microsoft Internet Explorer with ActiveX controls disabled will throw a warning prompt upon finding an object element (version(s) affected needed).

acknowledgements

Thanks to discussions and brainstorms with a bunch of folks: Ryan King, James Levine, the whole crowd at the Microformats specifications working session at MashupCamp, Brian Suda, Scott Reynen, Drew McLellan. Thanks to Mike Davies for accessibility research.

specifications using

considering

All class-based microformats SHOULD consider using and explicitly normatively stating support for the include pattern.

implementations

references

normative

  • HTML 4.01

informative

related pages

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