code: function initHighlightSlice() {
              highlightedSlice = svg.selectAll('.chart-group .arc path')
                  .select(filterHighlightedSlice).node();
  
              if (highlightedSlice) {
                  drawLegend(highlightedSlice.__data__);
                  tweenGrowth(highlightedSlice, externalRadius, pieDrawingTransitionDuration);
              }
          }
docs: Find the slice by id and growth it if needed
  @private