docs: def digest_prelude(self, rule):
          """
          Walk on rule prelude (aka CSS selector) tokens to return a string of
          the value name (from css selector).
  
          Actually only simple selector and selector with descendant combinator
          are supported. Using any other selector kind may leads to unexpected
          issues.
  
          Arguments:
              rule (tinycss2.ast.QualifiedRule): Qualified rule object as
                  returned by  tinycss2.
  
          Returns:
              string: Selector name. If it's a descendant combinator, items are
                  joined with ``__``.
          """
          name = []
  
          for token in rule.prelude:
              if token.type == 'ident':
                  name.append(token.value)
  
          return "__".join(name)