How to limit the fields that come back in a query

Query API calls like

http://api.cloudcms.com/docs#!/node/post_repositories_repositoryId_branches_branchId_nodes_query

support a parameter named _fields which defines an object specifying the node properties you want to include in the result set for matching nodes.

For example in the following query I want the title, subTitle and slug fields returned:

{
   "_type":"my:article", 
   "_fields":{
      "title":1,
      "subTitle":1,
      "slug":1
   }
}

The result set would look something like the following. Note that "_doc" is always returned for each node:

{
"rows": [{
"title": "Economics of Chronic Diseases",
"slug": "economics-of-chronic-diseases",
"subTitle": "",
"_doc": "5ce793471d775066206b"
}, {
"title": "EU governments weaken tobacco restrictions",
"slug": "eu-governments-weaken-tobacco-restrictions",
"subTitle": "",
"_doc": "d8a47dad5105d8e4e59e"
}, {
"title": "Dutch Supreme Court decision: all small bars and cafes must be 100% smoke free",
"slug": "dutch-supreme-court-decision-all-small-bars-and-cafes-must-be-100-smoke-free",
"subTitle": "",
"_doc": "d93eefdd94dfd5057c1c"
}
]