code: function updateChordVisibility(options) {
        if (options.mi && options.mi.show === true) {
          if (options.mi.index !== undefined) {
            chord.classed(
              'fade',
              (p) =>
                p.source.index !== options.mi.index &&
                p.target.index !== options.mi.index
            );
          } else {
            chord.classed('fade', false);
          }
          svg.selectAll('g.pmiChords path.pmiChord').classed('fade', true);
        } else if (options.pmi && options.pmi.show === true) {
          // Currently drawing pmi chords fades all mi chords, so we
          // don't have to do anything here to keep things consistent.
        }
      }
docs: Chord handling ---------------------------------------------------------