>One of:</p><ul><li><p><code>NULL</code> to use the default scale values</p></li>
<li><p>A character vector that defines possible values of the scale and their
order</p></li>
<li><p>A function that accepts the existing (automatic) values and returns
new ones. Also accepts rlang <a href="https://rlang.r-lib.org/reference/as_function.html" class="external-link">lambda</a> function
notation.</p></li>
</ul></dd>

    <dt><code>expand</code></dt>
<dd><p>For position scales, a vector of range expansion c