It is currently possible to hit the search handler in a streaming expression ("search(...)"), but it is not currently possible to invoke a streaming expression from within a regular search within the search handler. In some cases, it would be useful to leverage the power of streaming expressions to generate a result set and then join that result set with a normal set of search results.
This isn't expected to be particularly efficient for high cardinality streaming expression results, but it would be pretty powerful feature that could enable a bunch of use cases that aren't possible today within a normal search.
The current implementation also supports the following additional parameters:
f: (optional) The field name from the streaming expression containing the document ids upon which to filter. Defaults to the same uniqueKey field name from your documents.
method: (optional) Any of termsFilter (default), booleanQuery, automaton, docValuesTermsFilter.
The method may go away, especially if we find a more efficient way to join the stream to the main query doc set.