Hi,
I'm trying to find out the workflow of course filter (refine).

Up to now, i have already know:
When i click facets option(filter field rightside), course get searched via elasticsearch("search.elastic.ElasticSearchEngine") and refresh page via ajax,
and here is some program log.
iii. "POST /search/course_discovery/ HTTP/1.1" 200 33034
So, i checked 9200 port and it's elasticsearch and found that filter bar initial from search response.
If search response contains subject field(want to filter course by subject like math、cs), so it can shows subject facets on filter bar.
Finally, what i need is modify response of "/search/course_discovery/ HTTP/1.1".
But it seems did not appear at edx-platform subject, can anybody give some advice?
Thanks in advance and sorry for my poor english.