code: def _nest_rules(self, rule, scope, block):
          
          calculator = self._make_calculator(rule.namespace)
          raw_selectors = calculator.do_glob_math(block.prop)
          # DEVIATION: ruby sass doesn't support bare variables in selectors
          raw_selectors = calculator.apply_vars(raw_selectors)
          c_selectors, c_parents = self.parse_selectors(raw_selectors)
          if c_parents:
              warn_deprecated(
                  rule,
                  "The XCSS 'a extends b' syntax is deprecated.  "
                  "Use 'a { @extend b; }' instead."
              )
  
          new_ancestry = rule.ancestry.with_nested_selectors(c_selectors)
  
          rule.descendants += 1
          new_rule = SassRule(
              source_file=rule.source_file,
              import_key=rule.import_key,
              lineno=block.lineno,
              num_header_lines=block.header.num_lines,
              unparsed_contents=block.unparsed_contents,
  
              legacy_compiler_options=rule.legacy_compiler_options,
              options=rule.options.copy(),
              #properties
              extends_selectors=c_parents,
              ancestry=new_ancestry,
  
              namespace=rule.namespace.derive(),
              nested=rule.nested + 1,
          )
          self.rules.append(new_rule)
          rule.namespace.use_import(rule.source_file)
          self.manage_children(new_rule, scope)
  
          self._warn_unused_imports(new_rule)
docs: Implements Nested CSS rules