- - category for nest->vars[nest->n - 1], unless axis A's
- labels are moved to another axis
- - summary function, if 'a == t->summary_axis && t->slabels_axis ==
- t->summary_axis'
+ - category for nest->vars[nest->n - 1], unless t->label_axis[a] != a.
+ - summary function, if 'a == t->slabels_axis && a ==
+ t->summary_axis'.