diff --git a/docs/API_v3.md b/docs/API_v3.md
index 888cff84c..19c38415b 100644
--- a/docs/API_v3.md
+++ b/docs/API_v3.md
@@ -17,6 +17,8 @@ This file contains the API-Documentation. For more information on the returned D
 - By default, the API returns data formatted as _xml_. If formatting as _json_ is desired, the request should contain the header `Accept: application/json`. For simple representation, the output presented in this document is all formatted as _json_.
 - The OCS-Endpoint _always returns_ an object called `ocs`. This contains an object `meta` holding some meta-data, as well as an object `data` holding the actual data. In this document, the response-blocks only show the `data`, if not explicitely stated different.
 
+- OpenAPI spec: a machine-readable OpenAPI description is available at `/openapi.json` in the repository root. Prefer it as source-of-truth for exact request/response shapes.
+
 ```
 "ocs": {
   "meta": {
@@ -51,7 +53,7 @@ This file contains the API-Documentation. For more information on the returned D
     - `GET /api/v3/forms/{formId}/questions` to get all questions of a form
     - `GET /api/v3/forms/{formId}/questions/{questionId}` to get a single question
     - `POST /api/v3/forms/{formId}/questions/{questionId}/options` does now accept more options at once
-    - `PATCH /api/v3/forms/{formId}/questions/{questionId}/options/reorder` to reorder the options
+    - `PATCH /api/v3/forms/{formId}/questions/{questionId}/options` to reorder the options (request body `newOrder`, optional `optionType`)
     - `POST /api/v3/forms/{formId}/submissions/files/{questionId}` to upload a file to a file question before submitting the form
     - `GET /api/v3/forms/{formId}/submissions/{submissionId}` to get a single submission
     - `PUT /api/v3/forms/{formId}/submissions/{submissionId}` to update an existing submission
@@ -524,18 +526,23 @@ Contains only manipulative question-endpoints. To retrieve options, request the
   | _formId_ | Integer | ID of the form containing the question |
   | _questionId_ | Integer | ID of the question, the new option will belong to |
 - Parameters:
-  | Parameter | Type | Description |
-  |-----------|---------|-------------|
-  | _optionTexts_ | Array | Array of strings containing the new options |
-- Response: The new array of option objects
+ - Parameters:
+  | Parameter | Type | Optional | Description |
+  |-----------|---------|----------|-------------|
+  | _optionTexts_ | Array | | Array of strings containing the new options |
+  | _optionType_ | [Option Types](DataStructure.md#Option-Types) | yes | The option-type to assign to the new options (e.g. `row`). |
+ - Response: The new array of option objects
 
 ```
-"data": {
-  "id": 7,
-  "questionId": 1,
-  "order": 1,
-  "text": "test"
-}
+"data": [
+  {
+    "id": 7,
+    "questionId": 1,
+    "order": 1,
+    "text": "test",
+    "optionType": "choice"
+  }
+]
 ```
 
 ### Update option properties
@@ -579,7 +586,7 @@ Update a single or all properties of an option-object
 
 ### Reorder options
 
-- Endpoint: `/api/v3/forms/{formId}/questions/{questionId}/options/reorder`
+- Endpoint: `/api/v3/forms/{formId}/questions/{questionId}/options`
 - Method: `PATCH`
 - Url-Parameter:
   | Parameter | Type | Description |
@@ -590,6 +597,7 @@ Update a single or all properties of an option-object
   | Parameter | Type | Description |
   |-----------|---------|-------------|
   | _newOrder_ | Array | Array of **all** option IDs, ordered in the desired order |
+  | _optionType_ | [QuestionType](DataStructure.md#question-types) | *optional* option type to reorder (e.g. `row`). |
 - Restrictions: The Array **must** contain all option IDs corresponding to the specified question and **must not** contain any duplicates.
 - Response: Array of optionIds and their corresponding order.
 
@@ -919,6 +927,31 @@ Store Submission to Database
 
 - Response: **Status-Code OK**.
 
+### Update a Submission
+
+Update an existing submission (only allowed when `allowEditSubmissions` is set on the form).
+
+- Endpoint: `/api/v3/forms/{formId}/submissions/{submissionId}`
+- Method: `PUT`
+- Url-Parameters:
+  | Parameter | Type | Description |
+  |-----------|---------|-------------|
+  | _formId_ | Integer | ID of the form containing the submission |
+  | _submissionId_ | Integer | ID of the submission to update |
+- Parameters:
+  | Parameter | Type | Description |
+  |-----------|---------|-------------|
+  | _answers_ | Array | Array of answers (same structure as insert submission POST) |
+- Restrictions:
+    - The form must have `allowEditSubmissions` enabled.
+    - Only the user who created the submission may update it.
+    - Answers are validated the same way as on submit.
+- Response: **Status-Code OK**, as well as the id of the updated submission.
+
+```
+"data": 5
+```
+
 ### Delete a single Submission
 
 - Endpoint: `/api/v3/forms/{formId}/submissions/{submissionId}`
diff --git a/docs/DataStructure.md b/docs/DataStructure.md
index cdd2f8477..ed02cf97a 100644
--- a/docs/DataStructure.md
+++ b/docs/DataStructure.md
@@ -5,7 +5,7 @@
 
 # Forms Data Structure
 
-**State: Forms v3.3.1 - 08.10.2023**
+**State: Forms v5.3.0 - tbd**
 
 This document describes the Object-Structure, that is used within the Forms App and on Forms API v3. It does partially **not** equal the actual database structure behind.
 
@@ -120,19 +120,21 @@ The form state is used for additional states, currently following states are def
 
 Options are predefined answer-possibilities corresponding to questions with appropriate question-type.
 
-| Property   | Type    | Restrictions  | Description                                   |
-| ---------- | ------- | ------------- | --------------------------------------------- |
-| id         | Integer | unique        | An instance-wide unique id of the option      |
-| questionId | Integer |               | The id of the question, the option belongs to |
-| order      | Integer |               | The order of the option                       |
-| text       | String  | max. 1024 ch. | The option-text                               |
+| Property   | Type                          | Restrictions  | Description                                   |
+| ---------- | ----------------------------- | ------------- | --------------------------------------------- |
+| id         | Integer                       | unique        | An instance-wide unique id of the option      |
+| questionId | Integer                       |               | The id of the question, the option belongs to |
+| order      | Integer                       |               | The order of the option                       |
+| text       | String                        | max. 1024 ch. | The option-text                               |
+| optionType | [Option Types](#option-types) |               | The visual/semantic type of the option.       |
 
 ```
 {
   "id": 1,
   "questionId": 1,
   "order": 1,
-  "text": "Option 1"
+  "text": "Option 1",
+  "optionType": "choice"
 }
 ```
 
@@ -262,3 +264,18 @@ Optional extra settings for some [Question Types](#question-types)
 | `optionsHighest`        | `linearscale`                         | Integer          | `2, 3, 4, 5, 6, 7, 8, 9, 10`                | Set the highest value of the scale, default: `5`                            |
 | `optionsLabelLowest`    | `linearscale`                         | string           | -                                           | Set the label of the lowest value, default: `'Strongly disagree'`           |
 | `optionsLabelHighest`   | `linearscale`                         | string           | -                                           | Set the label of the highest value, default: `'Strongly agree'`             |
+| `columns`               | `grid`                                | Array            | -                                           | Array of column identifiers / labels for grid questions                     |
+| `rows`                  | `grid`                                | Array            | -                                           | Array of row identifiers / labels for grid questions                        |
+| `questionType`          | `grid`                                | String           | `checkbox`, `number`, `radio`               | Type of cell for grid questions (checkbox, numeric input, or radio)         |
+
+### Option Types
+
+Supported option types and their intended usage.
+
+| Type-ID  | Description                                                                                |
+| -------- | ------------------------------------------------------------------------------------------ |
+| `choice` | Standard selectable option used by `dropdown`, `multiple` and `multiple_unique` questions. |
+| `row`    | Represents a row header when rendering options in a grid-style question.                   |
+| `column` | Represents a column header when rendering options in a grid-style question.                |
+
+`row` and `column` option types are primarily used together with `grid` question types to build a two-dimensional selection matrix. `choice` is the default for normal option lists.
diff --git a/lib/ResponseDefinitions.php b/lib/ResponseDefinitions.php
index e71b0e51b..790ffe03c 100644
--- a/lib/ResponseDefinitions.php
+++ b/lib/ResponseDefinitions.php
@@ -12,7 +12,8 @@
  *   id: int,
  *   questionId: int|float,
  *   text: string,
- *   order: ?int
+ *   order: ?int,
+ *   optionType?: "choice"|"row"|"column"
  * }
  *
  * @psalm-type FormsOrder = array{
diff --git a/openapi.json b/openapi.json
index a423c4546..fdfe7600e 100644
--- a/openapi.json
+++ b/openapi.json
@@ -311,6 +311,14 @@
                         "type": "integer",
                         "format": "int64",
                         "nullable": true
+                    },
+                    "optionType": {
+                        "type": "string",
+                        "enum": [
+                            "choice",
+                            "row",
+                            "column"
+                        ]
                     }
                 }
             },