Card steps and cards: partial updates

sections/card_table_cards.md

@@ -394,7 +394,7 @@ _Optional parameters_:
 * `due_on` - due date (ISO 8601) of the card
 * `assignee_ids` - an array of people that will be assigned to this card. Please see the [Get people][people] endpoints to retrieve them.
 
-**Note:** omitting `title`, `content`, or `assignee_ids` leaves those values unchanged, but omitting `due_on` **clears** the due date. To keep an existing due date while changing something else, resend the current `due_on`.
+**Note:** this is a partial update — omitting any of `title`, `content`, `due_on`, or `assignee_ids` leaves it unchanged. To clear the due date, send `"due_on": null` explicitly; to remove all assignees, send `"assignee_ids": []`.
 
 This endpoint will return `200 OK` with the current JSON representation of the card if the update was a success. See the [Get a card](#get-a-card) endpoint for more info on the payload.
 

sections/card_table_steps.md

@@ -66,7 +66,13 @@ _Optional parameters_:
 * `assignee_ids` - an array of people ids that will be assigned to this step. Please see the [Get people][people] endpoints to retrieve them.
 * `assignees` - a comma separated list of people ids (legacy format, prefer `assignee_ids`).
 
-**Note:** this update **replaces** the step — any of `title`, `due_on`, or `assignee_ids` you omit is cleared. Resend the values you want to keep.
+**Note:** this is a partial update — any parameter you omit is left unchanged. To clear a value, send it explicitly:
+
+| To…                    | Send                     |
+| ---------------------- | ------------------------ |
+| leave a value unchanged | omit the parameter      |
+| clear the due date     | `"due_on": null`         |
+| remove all assignees   | `"assignee_ids": []`     |
 
 This endpoint will return `200 OK` with the current JSON representation of the step if the update was a success. See the step property of the [Get a card][card] endpoint for more info on the payload.