PUT /idx

    PUT /idx/mytype/_mapping
    {
        "properties": {
            "n1": {
                "type": "nested",
                "properties": {
                    "title": {
                        "type": "string"
                    },
                    "category": {
                        "type": "string"
                    }
                }
            }
        }
    }

    PUT /idx/mytype/_bulk
    {"index": {}}
    {"n1":{"title": "t1", "category": ["c1", "c3"]}}
    {"index": {}}
    {"n1":{"title": "t2", "category": ["c1", "c3"]}}
    {"index": {}}
    {"n1":{"title": "t3", "category": ["c2", "c3"]}}
    {"index": {}}
    {"n1":{"title": "t4", "category": ["c2", "c3"]}}
    {"index": {}}
    {"n1":{"title": "t5", "category": ["c2", "c3"]}}
    {"index": {}}
    {"n1":{"title": "t6", "category": ["c3"]}}