anchor.diff:  // 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
  -shard that it finds by sending an empty body for the request:
  -
  -[source,js]
  ---------------------------------------------------
  -GET /_cluster/allocation/explain
  ---------------------------------------------------
  -// CONSOLE
  -
  -[float]
  -==== Explain API Response
  -
  -This section includes examples of the cluster allocation explain API response output
  -under various scenarios.
  -
  -//////////////////////////
  +
  +===== Examples of unassigned primary shard explanations
   
   [source,js]
   --------------------------------------------------
  
positive.code: [[cluster-allocation-explain]]
  === Cluster Allocation Explain API
  
  The purpose of the cluster allocation explain API is to provide
  explanations for shard allocations in the cluster.  For unassigned shards,
  the explain API provides an explanation for why the shard is unassigned.
  For assigned shards, the explain API provides an explanation for why the
  shard is remaining on its current node and has not moved or rebalanced to
  another node.  This API can be very useful when attempting to diagnose why
  a shard is unassigned or why a shard continues to remain on its current node
  when you might expect otherwise.
  
  [float]
  ==== Explain API Request
  
  To explain the allocation of a shard, first an index should exist:
  
  [source,js]
  --------------------------------------------------
  PUT /myindex
  --------------------------------------------------
  // CONSOLE
  // TESTSETUP
  
  And then the allocation for shards of that index can be explained:
  
  [source,js]
  --------------------------------------------------
  
negative.code: --------------------------------------------------
  // CONSOLE
  
  
  ===== Example of the current_node parameter
  
  [source,js]
  --------------------------------------------------
  