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The itemid
global attribute is the unique, global identifier of an item. itemid
attributes can only be specified on elements that have both itemscope
and itemtype
attributes. Also, the itemid
can only be specified on elements with an itemscope
attribute whose corresponding itemtype refers to or defines a vocabulary that supports global identifiers.
An itemtype
's vocabulary will give the exact meaning of a global identifier defined within the vocabulary. The vocabulary will define whether several items with the same global identifier can co-exist and, if they are allowed, how items with the same identifier are handled.
Note: The Whatwg.org definition of an itemid
says that it must be a URL. This does not seem to be the case as the example below shows. Rather the defacto definition is that an itemid
is a unique identifier, so a URN is appropriate. This inconsistency no doubt reflects the incomplete nature of the Microdata specification.
Example
HTML
<dl itemscope itemtype="https://vocab.example.net/book" itemid="urn:isbn:0-330-34032-8"> <dt>Title <dd itemprop="title">The Reality Dysfunction <dt>Author <dd itemprop="author">Peter F. Hamilton <dt>Publication date <dd><time itemprop="pubdate" datetime="1996-01-26">26 January 1996</time> </dl>
Structured data
itemscope | itemtype: itemid |
https://vocab.example.net/book: urn:isbn:0-330-34032-8
|
|
itemprop | title | The Reality Dysfunction | |
itemprop | author |
Peter F. Hamilton
|
|
itemprop | pubdate | 1996-01-26 |
Result
Specifications
Specification | Status | Comment |
---|---|---|
itemid |
WG Note - No longer being actively developed |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|
Basic support | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |