revision:
It is used to activate/focus an element. Its lvalue must be a single character (a letter or a digit). The shortcut is varying in different browsers:
<element accesskey="character">
character: a single character that specifies the shortcut key to activate/focus the element.
<a href="https://lwitters.com" accesskey="l">lwitters (key: l)</a><br>
<a href="https://wikipedia.com" accesskey="w">Wikipedia (key: w)</a>
<a>If you need to relax, press the <strong><u>S</u></strong>tress reliever! /a>
<button accesskey="s">Stress reliever</button>