Incorrectly named file
Unknown if required...

http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/analysis-ngram-tokenfilter.html doesnt display the token_chars as an option but it's used in various articles and tracked in various queries on stackoverflow

* http://stackoverflow.com/questions/23374176/c-sharp-nest-elasticsearch-not-able-to-map-token-chars-to-nest-fluentmapping
* http://blog.qbox.io/multi-field-partial-word-autocomplete-in-elasticsearch-using-ngrams

Full copy of raw query being pushed in the article above here https://gist.github.com/ChrisMcKee/c4cab45080e52e35190a

(Obviously http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/analysis-ngram-tokenizer.html#analysis-ngram-tokenizer has it, so this may simply be a case of a common misunderstanding that ES casually lets fly)