docs: add params preference

docs/references/api/preferences.rst

@@ -13,8 +13,9 @@ The following preferences are supported.
 - ``Prefer: count``. See :ref:`prefer_count`.
 - ``Prefer: resolution``. See :ref:`prefer_resolution`.
 - ``Prefer: missing``. See :ref:`bulk_insert_default`.
-- ``Prefer: tx``. See :ref:`prefer_tx`.
 - ``Prefer: max-affected``, See :ref:`prefer_max_affected`.
+- ``Prefer: tx``. See :ref:`prefer_tx`.
+- ``Prefer: params``. See :ref:`prefer_params`.
 
 .. _prefer_handling:
 
@@ -295,3 +296,40 @@ To illustrate the use of this preference, consider the following scenario where
       "details": "The query affects 14 rows",
       "hint": null
   }
+
+.. _prefer_params:
+
+Single JSON object as Function Parameter
+----------------------------------------
+
+.. warning::
+
+  Using this preference is **deprecated** in favor of :ref:`s_proc_single_json`.
+
+:code:`Prefer: params=single-object` allows sending the JSON request body as the single argument of a :ref:`function <s_procs>`.
+
+.. code-block:: plpgsql
+
+  CREATE FUNCTION mult_them(param json) RETURNS int AS $$
+    SELECT (param->>'x')::int * (param->>'y')::int
+  $$ LANGUAGE SQL;
+
+.. tabs::
+
+  .. code-tab:: http
+
+    POST /rpc/mult_them HTTP/1.1
+    Prefer: params=single-object
+
+    { "x": 4, "y": 2 }
+
+  .. code-tab:: bash Curl
+
+    curl "http://localhost:3000/rpc/mult_them" \
+      -X POST -H "Content-Type: application/json" \
+      -H "Prefer: params=single-object" \
+      -d '{ "x": 4, "y": 2 }'
+
+.. code-block:: json
+
+  8