jquery/learn.jquery.com — pull request #252 by lsoares (2013-02-19 12:50:55+00:00)
Title: Update page/using-jquery-core/selecting-elements.md

Qualification (prefixation) is no longer useful; as the modern browsers have the document.querySelectAll() available, qualification even slows down the process.
Proof in:
http://jsperf.com/jquery-class-vs-tag-qualfied-class-selector/10