title: What exactly is the attribute in marshmallow.fields.Nested() function?
body: <p>I am trying to nest a Schema inside another Schema like the following:</p>
  
  <pre><code>class RecipePaginationSchema(PaginationSchema):
      data = fields.Nested(RecipeSchema, attribute = "items", many = True)
  </code></pre>
  
  <p>The result should look something like this: </p>
  
  <pre><code>{
      "links": {
          "first": "http://localhost:5000/users/name/recipes?per_page=2&amp;visibility=all&amp;page=1",
          "last": "http://localhost:5000/users/name/recipes?per_page=2&amp;visibility=all&amp;page=2",
          "next": "http://localhost:5000/users/name/recipes?per_page=2&amp;visibility=all&amp;page=2"
      },
      "page": 1,
      "pages": 2,
      "per_page": 2,
      "total": 3,
      "data": [
          {
              "id": 11,
              ...
          }
  }
  </code></pre>
  
  <p>However, when I tried to use another attribute instead of "items", I didn't get the "data" part in the JSON response. So, what exactly is this attribute thing referring to? </p>
  
  <p>By the way, I'm following Packt's Python API Development Fundamentals book.</p>