code: function unsafeToSkipNode(node) {
      switch (node.type) {
          case 'Rule':
              // unsafe skip ruleset with selector similarities
              return hasSimilarSelectors(node.prelude.children, this);
  
          case 'Atrule':
              // can skip at-rules with blocks
              if (node.block) {
                  // unsafe skip at-rule if block contains something unsafe to skip
                  return node.block.children.some(unsafeToSkipNode, this);
              }
              break;
  
          case 'Declaration':
              return false;
      }
  
      // unsafe by default
      return true;
  }
docs: test node can't to be skipped