ls. However, if you want to calculate
intervals for some function <code>y = f(x)</code> conditional on some other variable(s) (say, conditional on a
factor <code>g</code>), you would group by <code>g</code>, then use <code>.along = x</code> to calculate intervals jointly over <code>x</code>
conditional on <code>g</code>. To avoid selecting any variables as input values to the function describing the
curve, use <code><a href="https://rdrr.io/r/base/character.html" class="external-link">character()</a></code>