docs: def _extract_special(current, table_data):
      """
      Extract year, age, and depth column from table data
      :param dict table_data: Data at the table level
      :param dict current: Current data
      :return dict current:
      """
      logger_ts.info("enter extract_special")
      try:
          # Add age, year, and depth columns to ts_root where possible
          for k, v in table_data['columns'].items():
              s = ""
  
              # special case for year bp, or any variation of it. Translate key to "age""
              if "bp" in k.lower():
                  s = "age"
  
              # all other normal cases. clean key and set key.
              elif any(x in k.lower() for x in ('age', 'depth', 'year', "yr", "distance_from_top", "distance")):
                  # Some keys have units hanging on them (i.e. 'year_ad', 'depth_cm'). We don't want units on the keys
                  if re_pandas_x_und.match(k):
                      s = k.split('_')[0]
                  elif "distance" in k:
                      s = "depth"
                  else:
                      s = k
  
              # create the entry in ts_root.
              if s:
                  try:
                      current[s] = v['values']
                  except KeyError as e:
                      # Values key was not found.
                      logger_ts.warn("extract_special: KeyError: 'values' not found, {}".format(e))
                  try:
                      current[s + 'Units'] = v['units']
                  except KeyError as e:
                      # Values key was not found.
                      logger_ts.warn("extract_special: KeyError: 'units' not found, {}".format(e))
  
      except Exception as e:
          logger_ts.error("extract_special: {}".format(e))
  
      return current