.r-lib.org/reference/language.html" class="external-link">tidyselect</a>&gt; Which columns are the input values to the function
describing the curve (e.g., the "x" values). Intervals are calculated jointly with
respect to these variables, conditional on all other grouping variables in the data frame. The default
(<code>NULL</code>) causes <code>curve_interval()</code> to use all grouping variables in the input data frame as the value
for <code>.along</code>, which will generate the most conservative interva