section-exercises here is the @kind of section (same as "howto" etc). We have not yet designed a way to describe slots which specifically target kinds of the parent contexts. Eg, "this is an image inside a specific kind of feature" so the elements like exercises in this section have an ugly section-exercise @context (#content>#figure>.style(@kind; @part; problem; exercise; section-exercise), "a figure in a problem in an exercise in the 'Section Exercises' kind of section").