Simply, the specification for custom data attributes states that any attribute that starts with "data-" will be treated as a storage area for private data (private in the sense that the end user can't see it - it doesn't affect layout or presentation).
This allows you to write valid HTML markup (passing an HTML 5 validator) while, simultaneously, embedding data within your page
M. Schindler, и D. Vrandecic. Proceedings of the WebSci'09: Society On-Line, Web Science Overlay Journal, (марта 2009)http://journal.webscience.org/213/1/websci09_submission_120.pdf.
T. Malone, R. Laubacher, и C. Dellarocas. Research Paper, No. 4732-09. MIT, Sloan School of Management, Massachusetts Institute of Technology, Cambridge, MA, USA, (февраля 2009)