title: What is the @_(get: "edges") notation?
body: <p>I am relatively new to GraphQL and have seen some notations like  <code>@_(get: "edges")</code> in our GraphQL queries. We are using Apollo and PostGraphile. I have tried looking for some documentation on this, however can't seem to find any. Other things I have seen are: 
  <code>@_(get: "edges", flattenDepth: 1, groupBy: "contentType")</code></p>