code: private static HashMap<String, Double> cmmlNodeToHistrogram(Node node, String tagName) throws XPathExpressionException {
          final NodeList elements = XMLHelper.getElementsB(node, "*//*:" + tagName);
          return contentElementsToHistogram(elements);
      }
docs: converts content math ml to a histogram for the given tagname, e.g., cn
  
  @param node
  @param tagName
  @return