It's not clear from the website's documentation, or the --help output, how to do the following equivalent curl task:

Post a raw JSON query to ElasticSearch:

curl \
    --header "Content-Type: application/json" \
    --request POST \
    --data '{ "_source": [ "restricted_countries.*" ], "query": { "match_all": {} }, "size": 1000 }' \
    'http://localhost:9200/_search'

The examples seem to show how to post form values and other stuff.

It would be great if there was a way to do this, and if it was documented in all places, such that searching for "httpie post json" would show the answer in the search result context of Google's top hits.

After a quick read of the documentation, I'm not even sure if it's possible, but I didn't dig that deep.