t option <code>"alluvia"</code> to bind aesthetics after stratifying by
the index axis but before stratifying by linked axes (only available for
<code>stat_alluvium()</code>). Stratification by any axis is done with respect to the
strata at that axis, after separating positive and negative strata,
consistent with the values of <code>decreasing</code>, <code>reverse</code>, and <code>absolute</code>.
Thus, if <code>"none"</code>, then lode orderings will not depend on aesthetic
variables. All aesthetic varia