docs: function computeFixedSize(nodes, referenceSize) {
      var fixedSize = "";
      nodes.forEach(function (node) {
          var ratio = node.attribs['cell-ratio'];
          if (typeof ratio === 'undefined') return;
          var size = referenceSize + '*' + ratio;
          if (fixedSize != '') fixedSize += '+';
          fixedSize += size;
          node.size = size;
      });
      return fixedSize;
  }