docs: function normalizeProperty(element, slotName) {
      var type, normalized;
  
      if (slotName in element) {
        normalized = slotName;
        type = 'prop';
      } else {
        var lower = slotName.toLowerCase();
        if (lower in element) {
          type = 'prop';
          normalized = lower;
        } else {
          type = 'attr';
          normalized = slotName;
        }
      }
  
      if (type === 'prop' && (normalized.toLowerCase() === 'style' || preferAttr(element.tagName, normalized))) {
        type = 'attr';
      }
  
      return { normalized: normalized, type: type };
    }