Is there a structure builder example where the format of each preview for the document list is modified?

export default {
  name: "review",
  title: "Review",
  type: "document",
  fields: [
    {
      name: "content",
      title: "Content",
      type: "object",
      fields: [
        {
          name: 'title',
          title: 'Title',
          type: 'string',
        },
        {
          name: 'excerpt',
          title: 'Excerpt',
          type: 'string',
        }
      ]
    },
  ],
}

export default {
  name: "review",
  title: "Review",
  type: "document",
  fields: [
    {
      name: "content",
      title: "Content",
      type: "object",
      fields: [
        {
          name: 'title',
          title: 'Title',
          type: 'string',
        },
        {
          name: 'excerpt',
          title: 'Excerpt',
          type: 'string',
        }
      ]
    },
  ],
  preview: {
    select: {
      title: 'content.title'
    }
  }
}