curl -XPUT 'localhost:9200/test/test/1?pretty' -H 'Content-Type: application/json' -d' {
    ".foo" : {
        "foo" : {
            "bar" : 123 
        }
    } 
}
'

{
  "error" : {
    "root_cause" : [
      {
        "type" : "mapper_parsing_exception",
        "reason" : "failed to parse"
      }
    ],
    "type" : "mapper_parsing_exception",
    "reason" : "failed to parse",
    "caused_by" : {
      "type" : "illegal_argument_exception",
      "reason" : "object field starting or ending with a [.] makes object resolution ambiguous: [.foo]"
    }
  },
  "status" : 400
}

curl -XPUT 'localhost:9200/test/test/1?pretty' -H 'Content-Type: application/json' -d' {
    "foo." : {
        "foo" : {
            "bar" : 123 
        }
    } 
}
'

{
  "_index" : "test",
  "_type" : "test",
  "_id" : "1",
  "_version" : 9,
  "result" : "updated",
  "_shards" : {
    "total" : 2,
    "successful" : 1,
    "failed" : 0
  },
  "_seq_no" : 8,
  "_primary_term" : 1
}

curl -XGET 'localhost:9200/test/test/1'
{ "_index":"test","_type":"test","_id":"1","_version":9,"found":true,"_source": {
"foo." : {
    "foo" : {
        "bar" : 123 
    }
} 
}