function collectedHist = attachToDom(obj, dom, parent, collectedHist)
  
  collectedHist = attachToDom@data2D(obj, dom, parent, collectedHist);
  
  % Add zunits
  if isa(obj.zunits, 'unit')
    zunitsNode = dom.createElement('zunits');
    collectedHist = obj.zunits.attachToDom(dom, zunitsNode, collectedHist);
    parent.appendChild(zunitsNode);
  end
  
  % Add z
  zNode = dom.createElement('z');
  utils.xml.attachNumberToDom(obj.z, dom, zNode)
  parent.appendChild(zNode);
  
end