Chapter 6. Microdata and Custom Data

Kimberly Blessing


One of the primary benefits of web standards, promoted for over 10 years by standards evangelists, was that more semantic markup would provide greater context and meaning to content.

By the mid 2000s, web standards were catching on, but the “standardistas” recognized that semantic markup alone was not enough to convey all meaning related to content—for example, that some content is personal data or that links may represent relationships.

To solve this problem, first came XFN (XHTML Friends Network, see, and then microformats (see Both of these solutions relied on the class and rel attributes—both valid (X)HTML—but, because those attributes had more appropriate uses, some web professionals felt that using them to convey additional semantics was somewhat of a hack.

At about the same time, the W3C XHTML 2 Working Group created the RDFa specification, based on the Resource Description Framework, to enable reuse of existing XHTML attributes—and the addition of some new ones—to support structured machine-readable data.

Microformats, in particular, caught on quickly with web professionals. Web builders started using them to mark up personal information, resumes, event data, and even cooking recipes. Search engines picked up on this and began parsing the additional data found in microformats and RDFa to improve search results.

With HTML5, the web community has a renewed focus on ...

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