anchor.diff:  [float]
   === Explain API Request
   
  -To explain the allocation of a shard, issue a request:
  -
  -[source,js]
  ---------------------------------------------------
  -$ curl -XGET 'http://localhost:9200/_cluster/allocation/explain' -d '{
  +To explain the allocation of a shard, first an index should exist:
  +
  +[source,js]
  +--------------------------------------------------
  +PUT /myindex
  +--------------------------------------------------
  +// TESTSETUP
  +
  +And then the allocation for shards of that index can be explained:
  +
  +[source,js]
  +--------------------------------------------------
  +GET /_cluster/allocation/explain
  +{
     "index": "myindex",
     "shard": 0,
     "primary": true
  -}'
  ---------------------------------------------------
  +}
  +--------------------------------------------------
  +// CONSOLE
   
   Specify the `index` and `shard` id of the shard you would like an explanation
   for, as well as the `primary` flag to indicate whether to explain the primary
  
positive.code: 
  [source,js]
  --------------------------------------------------
  $ curl -XGET 'http://localhost:9200/_cluster/allocation/explain'
  --------------------------------------------------
  
  [float]
  === Explain API Response
  
negative.code: 
  [source,js]
  --------------------------------------------------
  GET /_cluster/allocation/explain
  {
    "index": "myindex",
    "shard": 0,
    "primary": false,
    "current_node": "nodeA"                         <1>
  }
  --------------------------------------------------
  // CONSOLE
  // TEST[skip:no way of knowing the current_node]
  <1> The node where shard 0 currently has a replica on
  
  You can also have Elasticsearch explain the allocation of the first unassigned
  