If I understood it correctly an FST is created per segment for every completion suggester.
Suppose we would want to write an Elasticsearch plugin that would allow us to intersect a given automaton (i.e. search logic you can’t express with a regular expression) with these FSTs, where can I (having no knowledge of the inner workings of Elasticsearch) find some sample code (or other information) to access these FSTs created by Elasticsearch.
I think I found it: CompletionSuggester line 86 -> CompletionScorer (Lucene) -> NRTSuggester (Lucene).
And I guess the example plugins contain enough sample code to start writing our own plugin.
Confirmation or other feedback is still welcome though.