The itemid global attribute provides microdata in the form of a unique, global identifier of an item.

An itemid attribute can only be specified for an element that has both itemscope and itemtype attributes. Also, itemid can only be specified on elements that possess an itemscope attribute whose corresponding itemtype refers to or defines a vocabulary that supports global identifiers.

The exact meaning of an itemtype's global identifier is provided by the definition of that identifier within the specified vocabulary. The vocabulary defines whether several items with the same global identifier can coexist and, if so, how items with the same identifier are handled.

Note: The WHATWG definition specifies that an itemid must be a URL. However, the following example correctly illustrates that a URN may also be used. This inconsistency may reflect the incomplete nature of the Microdata specification.


Representing structured data for a book

This example uses microdata attributes to represent the following structured data:

itemscope itemtype: itemid urn:isbn:0-374-22848-5
itemprop title Owls of the Eastern Ice
itemprop author Jonathan C Slaght
itemprop datePublished 2020-08-04


  <dd itemprop="title">Owls of the Eastern Ice</dd>
  <dd itemprop="author">Jonathan C Slaght</dd>
  <dt>Publication date</dt>
    <time itemprop="datePublished" datetime="2020-08-04">August 4 2020</time>



HTML Standard
# attr-itemid

See also