docs: def _cdata_header(self, colsep="|"):
          """
          Create a header for the CDATA section, as a visual guide.
          """
          fields = self.fields
          header_lines = []
          line = ""
          for fieldName in self.field_names:
              width = int(fields[fieldName]['attr']['width'])
              line += self._entry(fieldName, width, colsep)
          header_lines.append(line)
  
          line = ""
          for fieldName in self.field_names:
              width = int(fields[fieldName]['attr']['width'])
              line += self._entry(fields[fieldName]['attr']['format'], width=width, colsep=colsep)
          header_lines.append(line)
  
          line = ""
          for fieldName in self.field_names:
              width = int(fields[fieldName]['attr']['width'])
              (l, m) = divmod(width, 10)
              guide = ""
              for i in range(l):
                  guide += "".join(map(str, range(10)))
              guide += "".join(map(str, range(m)))
              line += self._entry(guide, width=width, colsep=colsep)
          header_lines.append(line)
  
          line = ""
          for fieldName in self.field_names:
              width = int(fields[fieldName]['attr']['width'])
              guide = "-" * width
              line += self._entry(guide, width=width, colsep=colsep)
          header_lines.append(line)
  
          return header_lines