Returning specific attributes with GraphQL

I'm trying to use the GraphQL API to return a single attribute along with the _id, rather than the entire document. According to the documentation, the following should work:

query { databasesListDocuments( databaseId: "${DATABASE_ID}", collectionId: "${COLLECTION_ID}" ) { total documents { _id data { attribute1 } } } }

However, I'm getting the following error:

Response: {"errors":[{"message":"Field "data" of type "String" must not have a sub selection.","extensions":{"category":"graphql"},"locations":[{"line":9,"column":16}]}]}

The following doesn't work either:

query { databasesListDocuments( databaseId: "${DATABASE_ID}", collectionId: "${COLLECTION_ID}" ) { total documents { _id attribute1 } } }

Any ideas what I'm doing wrong?