A pull quote is a typographical technique in which an excerpt or quote from an article is duplicated within the article using a different formatting style so that it jumps out at the reader.
Blatantly copying the excerpt of the pull quote into it’s own element is not the way to go. A pull quote is a purely visual technique, and therefore should not change the structure of the body. Next to that, a structural representation of the excerpt would be seen twice by people using feed readers or services like Instapaper, as well as be re-read for people who use screen readers. So how can we best author this into our mark-up?
HTML5 introduced the ability for authors to create custom non-visible data-attributes. These attributes can contain data that will not affect layout or presentation.
Custom data attributes are intended to store custom data private to the page or application, for which there are no more appropriate attributes or elements.
By adding a data-pullquote attribute to an element, we attach the text of the pull quote to it, yet do not add visible content.
Original source: http://miekd.com/articles/pull-quotes-with-html5-and-css/