docs: def load_data(self, filename, *args, **kwargs):
          """
          Load text data from different sheets.
          """
          # load text data
          data = super(MixedTextXLS, self).load_data(filename)
          # iterate through sheets in parameters
          for sheet_params in self.parameters.itervalues():
              # iterate through the parameters on each sheet
              for param, pval in sheet_params.iteritems():
                  pattern = pval.get('pattern', EFG_PATTERN)  # get pattern
                  re_meth = pval.get('method', 'search')  # get re method
                  # whitelist re methods, getattr could be considered harmful
                  if re_meth in RE_METH:
                      re_meth = getattr(re, pval.get('method', 'search'))
                  else:
                      msg = 'Only', '"%s", ' * len(RE_METH) % tuple(RE_METH)
                      msg += 'regex methods are allowed.'
                      raise AttributeError(msg)
                  # if not isinstance(data[param], basestring):
                  #     re_meth = lambda p, dp: [re_meth(p, d) for d in dp]
                  match = re_meth(pattern, data[param])  # get matches
                  if match:
                      try:
                          match = match.groups()
                      except AttributeError:
                          match = [m.groups() for m in match]
                      npdata = np.array(match, dtype=float).squeeze()
                      data[param] = npdata * UREG(str(pval.get('units') or ''))
                  else:
                      raise MixedTextNoMatchError(re_meth, pattern, data[param])
          return data