using label element for associating extra descriptive text

label

example 1 single label wraps primary label text and auxiliary label text results 
in accessible name for the control being the a concatenation of the primary and auxiliary label text.

conforming:
<label>name <input type"text"> last name only please</label>

example 2 primary label = accessible name, auxiliary label = accessible description

conforming:
<p><label>name <input type"text" aria-describedby="instructions"></label></p>
<p><label id="instructions">last name only please</label></p>


non-conforming:

<label>poot</label>  <input>