[DOCS] Clarified docs for cluster.routing.allocation.same_shard.host cluster setting

Clarified also javadocs for SameShardAllocationDecider

docs/reference/modules/cluster.asciidoc

@@ -56,9 +56,10 @@ The following settings may be used:
     deprecated[1.0.0.RC1,Replaced by `cluster.routing.allocation.enable`]
 
 `cluster.routing.allocation.same_shard.host`::
-      Prevents that multiple instances of the same shard are allocated
-      on a single host. Defaults to `false`. This setting only applies
-      if multiple nodes are started on the same machine.
+      Allows to perform a check to prevent allocation of multiple instances
+      of the same shard on a single host, based on host name and host address.
+      Defaults to `false`, meaning that no check is performed by default. This
+      setting only applies if multiple nodes are started on the same machine.
 
 `indices.recovery.concurrent_streams`::
        The number of streams to open (on a *node* level) to recover a

src/main/java/org/elasticsearch/cluster/routing/allocation/decider/SameShardAllocationDecider.java

@@ -28,14 +28,18 @@ import org.elasticsearch.common.inject.Inject;
 import org.elasticsearch.common.settings.Settings;
 
 /**
- * An allocation decider that prevents multiple instances of the same shard to be
- * allocated on a single <tt>host</tt>. The cluster setting can be modified in
- * real-time by updating the {@value #SAME_HOST_SETTING} value of cluster setting
- * API. The default is <code>false</code>.
+ * An allocation decider that prevents multiple instances of the same shard to
+ * be allocated on the same <tt>node</tt>.
+ *
+ * The {@value #SAME_HOST_SETTING} setting allows to perform a check to prevent
+ * allocation of multiple instances of the same shard on a single <tt>host</tt>,
+ * based on host name and host address. Defaults to `false`, meaning that no
+ * check is performed by default.
+ *
  * <p>
  * Note: this setting only applies if multiple nodes are started on the same
- * <tt>host</tt>. Multiple allocations of the same shard on the same <tt>node</tt> are
- * not allowed independent of this setting.
+ * <tt>host</tt>. Allocations of multiple copies of the same shard on the same
+ * <tt>node</tt> are not allowed independently of this setting.
  * </p>
  */
 public class SameShardAllocationDecider extends AllocationDecider {