code: function nodesOverlap (nodeA, nodeB) {
      // test if nodeA top partially overlaps nodeB
      if (nodeA.y0 > nodeB.y0 && nodeA.y0 < nodeB.y1) {
        return true
      } else if (nodeA.y1 > nodeB.y0 && nodeA.y1 < nodeB.y1) {
        // test if nodeA bottom partially overlaps nodeB
        return true
      } else if (nodeA.y0 < nodeB.y0 && nodeA.y1 > nodeB.y1) {
        // test if nodeA covers nodeB
        return true
      } else {
        return false
      }
    }
docs: check if two nodes overlap