code: function walkAndFormat(node) {
    if (node) {
      if (node.append !== 'once') {
        if (node.children && node.children.length) {
          for (var i = 0, len = node.children.length; i < len; i++) {
            walkAndFormat(node.children[i])
          }
        }
      }
      else {
        format(node)
      }
    }
  }
docs: walk all nodes and format richtext root node
  
  @param  {Node} node