Recognizing Semantics - HTML5 Mastery: Semantics, Standards, and Styling - page 117

Note The WHATWG HTML specification defines a ping attribute for links ( a ele-
ments and area elements—covered in Chapter 5 ) for defining URLs that should be
notified when a link is visited. However, there is controversy over its inclusion (over
concern it could be abused), and the W3C version of the HTML5 specification does not
include this attribute. Until this is sorted out, you're best leaving this attribute alone for
the time being.
Emphasis and importance: em and strong
While web browsers will usually display an em and strong with italic and bold text,
respectively, these elements should not be viewed as a means to bold or italicize text,
because that presentational function should be left to CSS style sheets; rather, the em