code: def resolve(container, expression):
      
      itemgetter = getattr(container, 'get_item', container.get)
      tokens = []
      expression = expression.strip()
      for sel_delim, _id, _range in selection_re.findall(expression):
          tokens.append(delimiters.get(sel_delim, ''))
          item = itemgetter(_id)
          if item is None:
              raise XigtStructureError(
                  'Referred Item (id: {}) from reference "{}" does not '
                  'exist in the given container.'
                  .format(_id, expression)
              )
          # treat None values as empty strings for resolution
          value = item.value() or ''
          if _range:
              for spn_delim, start, end in span_re.findall(_range):
                  start = int(start) if start else None
                  end = int(end) if end else None
                  tokens.extend([
                      delimiters.get(spn_delim, ''),
                      value[start:end]
                  ])
          else:
              tokens.append(value)
      return ''.join(tokens)
docs: Return the string that is the resolution of the alignment expression
      `expression`, which selects ids from `container`.