Update reference docs for Highlighter fragmenter

[sudo-suhas]

Highlighting supports an option fragmenter which is supported by the Plain fragmenter but the reference documentation does not mention it.

Reference documentation for the same was added by collating information from the following sources:

• Expose fragmenter option for plain highlighter Expose fragmenter option for plain highlighter #2465
• Lucene docs for Fragmenter, NullFragmenter, SimpleFragmenter and SpansHighlighter
• Elasticsearch source code for PlainHighlighter
• Discussion in the issue Incomplete reference documentation for 'Highlighting' #23736

Closes #23736

[elasticmachine]

Since this is a community submitted pull request, a Jenkins build has not been kicked off automatically. Can an Elastic organization member please verify the contents of this patch and then kick off a build manually?

[sudo-suhas]

@javanna Does this documentation look okay?

[javanna]

hi @sudo-suhas the addition looks good thanks! The json is malformed though, which makes our build fail as we validate json snippets. You can reproduce that by running gradle check from the docs directory in our repo. Would you have time to also add the response and compare the two different options available?

[sudo-suhas]

Ah.. Should have paid more attention while copying. Also, did not realise docs had a gradle build. Will do the check before committing next time. For giving the response and compare, can you suggest an appropriate example from the examples repo? I have loaded the NYC accident data and NGINX logs previously but I don't think they will be appropriate for this exercise.

[javanna]

@sudo-suhas start with fixing your query. as for examples, I would look in our docs and take inspiration from there.

[sudo-suhas]

@javanna I have pushed a commit with requested changes. However, setup of gradle, running tests, setting up test indices etc was non-trivial. I think it would be good if there was a slightly more detailed guide for contributors. I have created a gist here with CONSOLE script for setting up the test indices for anybody else who might want to use it.

[sudo-suhas]

@javanna Are there any changes required for this pull request? I wanted to get 1 right before doing the changes in the other pull request.

[javanna]

jenkins test this please

[javanna]

jenkins retest this please

[sudo-suhas]

@javanna I know this is probably a low priority. However, please note that I have modified only one file in docs for which I ran the gradle docs:check as suggested. Is there anything I need to do to fix the failing build?

[nik9000]

It looks like @javanna is doing something else. I reviewed and it looks good. I'll test it locally and merge if all looks good.

[nik9000]

I've merged to master and cherry-picked to 5.x and 5.4.

[nik9000]

Thanks @sudo-suhas! The docs really did look nice.

[sudo-suhas]

@nik9000 Does it need to be cherry-picked to 5.3 as well? Docs not visible here https://www.elastic.co/guide/en/elasticsearch/reference/5.3/search-request-highlighting.html or https://www.elastic.co/guide/en/elasticsearch/reference/current/search-request-highlighting.html

[javanna]

thanks @nik9000 and @sudo-suhas !

[nik9000]

Does it need to be cherry-picked to 5.3 as well?

I was trying not to push anything to 5.3 because we're trying to keep it stable. But I already pushed a bunch of docs to it last night so I'm happy to cherry-pick there.