value-class-pattern

Value Excerption Pattern

The value excerption pattern is derived from value-excerpting in hCard. As such, it is already somewhat supported in parsers. However, the precise parsing behaviour is not yet finalised, so the pattern should be used only with extreme caution, and with the awareness that the editing of more precise parsing rules could impact your pages.

Editor

Ben Ward

Sometimes, only a part of an element's content is used as the value of a microformat property. This may occur when a property has optional sub-properties, such as tel in hCard. Other times, the most logical, semantic element for the property class name may include other content.

For these purposes, the special class name value is used to excerpt out the relevant element content.

Simple Examples

Here is an hCard fragment for marking up a home phone number:

vCard:

<code>TEL;TYPE=HOME:+1.415.555.1212</code>

hCard:

<code>
 <span class="tel">
   <span class="type">Home</span>:
   <span class="value">+1.415.555.1212</span>
 </span>
</code>

In this case, the value of tel is +1.415.555.1212, not Home: +1.415.555.1212.

Another example, this time using price in hListing:

<code>
 <span class="price">
    I want to sell for
    <span class="value">£15</span>
 </span>
</code>

In this case, price will parse as £15, rather than as the entire sentence.

Another example, using dtstart in hCalendar:

<code>
 <span class="dtstart">
    Friday 25th May, 6pm
    <span class="value">2008-05-25T18:00:00+0100</span>
 </span>
</code>

Whilst the entire string ‘Friday 25th May […]’ is semantically the date, it's the ISO 8601 encoded form alone which must be consumed by a microformats parser, so the value class isolates it.

Parsing

• Where an element with a microformat property class name has an descendant with class name value, parsers should read the inner-text of the value element only, ignoring other text node descendants.
• Where multiple descendants of a property all have a class name of value, they should be concatenated, without inserting additional characters or white-space.
• Where an element foo with class value has a descendant bar with class value, the entire content of foo is taken as the value. Nesting additional elements with class of value cannot be used to further isolate a property's value.

There is a draft flow chart showing the parsing behaviour for value-excerption, including proposed empty-node parsing: Value Excerption Parsing Flow Chart (out of date).

Related Pages

• value-excerption-pattern-issues
• hCard: Value Excepting
• Machine Data in Microformats