code: function calcVerticalBuffer (links, circularLinkGap, id) {
      links.sort(sortLinkColumnAscending)
      links.forEach(function (link, i) {
        var buffer = 0
  
        if (selfLinking(link, id) && onlyCircularLink(link)) {
          link.circularPathData.verticalBuffer = buffer + link.width / 2
        } else {
          var j = 0
          for (j; j < i; j++) {
            if (circularLinksCross(links[i], links[j])) {
              var bufferOverThisLink =
                links[j].circularPathData.verticalBuffer +
                links[j].width / 2 +
                circularLinkGap
              buffer = bufferOverThisLink > buffer ? bufferOverThisLink : buffer
            }
          }
  
          link.circularPathData.verticalBuffer = buffer + link.width / 2
        }
      })
  
      return links
    }
docs: creates vertical buffer values per set of top/bottom links