ElasticSearch ID constraints

Slash "/" URL encoding is broken: https://github.com/elasticsearch/elasticsearch/issues/2903

Slash "/" is no longer broken. This issue has been fixed.

There are no constraints. Forward slashes can be used. But in order to use such id in the REST API, it has to be url encoded:

$ curl -XPUT "localhost:9200/id-test-index/rec/1+1%2F2" -d '{"field" : "one and a half"}'