i><p>A function that takes the breaks as input and returns labels
    as output</p></li>
</ul></dd>


<dt>limits</dt>
<dd><p>A numeric vector of length two providing limits of the scale.
Use <code>NA</code> to refer to the existing minimum or maximum.</p></dd>


<dt>expand</dt>
<dd><p>A numeric vector of length two giving multiplicative and
additive expansion constants. These constants ensure that the data is
placed some distance away from the axes. The defaults are
<code>c(0.05, 0)</code> for continuous va