Microdata (HTML)

Microdata is a WHATWG specification for nesting machine-readable metadata inside ordinary HTML. It was proposed by Ian Hickson in 2009 as part of the HTML5 work, after the WHATWG declined to incorporate <a href="/knowledge/rdfa" class="link" style="color: #D4A843;" title="Direct link to chunk">RDFa</a> into the HTML5 specification. The W3C published a parallel Microdata Note in 2013 but stopped maintaining it for lack of an editor; the canonical text now lives in the WHATWG HTML Living Standard. Authors annotate elements with five core attributes. itemscope marks an element as a structured item, itemtype names the vocabulary (usually a <a href="/knowledge/Schema.org" class="link" style="color: #D4A843;" title="Direct link to chunk">Schema.org Structured Data</a> URL) describing the item, itemprop labels a property within that item, itemid gives the item a global identifier, and itemref pulls in properties from elsewhere in the document. Because every attribute lives on an existing HTML element, the same markup serves both human display and machine extraction. Microdata was the original encoding endorsed by Schema.org at its 2011 launch and remains a supported choice for structured data alongside <a href="/knowledge/json-ld" class="link" style="color: #D4A843;" title="Direct link to chunk">JSON-LD</a> and RDFa. Search engines including Google, Bing, Yahoo and Yandex still parse it for rich results. In practice it has lost ground to JSON-LD because nesting deep object graphs as itemscope blocks is verbose, brittle, and entangled with presentational markup, while JSON-LD lives in a single script element that is easier for templates and component frameworks to emit and update.