I'm not entirely sure where this links to, did a quick grep in the es repo and couldn't dig it up but I suppose its a general painless script page. When looking at the code about which kind of scripts are allowed here I was suprised to see that this is a specific kind of script (in the code called AnalysisPredicateScript) that seems to be limited to work on certain token attributes (like length, position etc...) only. Maybe its worth mentioning that this only works on token properties (so looks like "token.*" would always be the first part in the chain). @jdconrad should be able to validate this assumption.

Thanks @cbuescher. For clarity, this currently links here:
https://www.elastic.co/guide/en/elasticsearch/reference/master/modules-scripting-using.html#_script_parameters

That content covers generic parameters for the script object. They aren't specific to Painless.

I think that link is still probably the best place to get those generic parameters, but I can also link to this page for Painless scripts used in this parameter:
https://www.elastic.co/guide/en/elasticsearch/painless/current/painless-analysis-predicate-context.html

Would that work for you @cbuescher @jdconrad? If only Painless scripts are allowed here, I can try another approach.

Made these proposed changes in 4d127da and 77a5dd9 to make review a bit easier.

Script contexts are supposed to be generic, so I would prefer to try to document them as such. I don't have a strong opinion one way or another on a link to Painless docs.

Maybe add a short comment after this example explaining what this analyzer does, its pretty obvious from the analyzer name but for some folks it might be worth spelling it out.

Thank you for the comment! I was debating whether that was needed.

I added a description to the preceding paragraph with 3653233.