title: What is an exclamation point in GraphQL?
body: <p>In a schema file that I have I noticed there are exclamation marks after some types, like</p>
  
  <pre><code># Information on an account relationship
  type AccountEdge {
    cursor: String!
    node: Account!
  }
  </code></pre>
  
  <p>What do these mean? I can't find anything about it in the documentation or through googling </p>