feat(block-kit): add attachment_mention block element example

block-kit/README.md

@@ -24,3 +24,7 @@ Read the [docs](https://docs.slack.dev/block-kit/) to learn concepts behind thes
 - **[Table](https://docs.slack.dev/reference/block-kit/blocks/table-block)**: Displays structured information in a table. [Implementation](./src/blocks/table.py).
 - **[Task card](https://docs.slack.dev/reference/block-kit/blocks/task-card-block)**: Displays a single task, representing a single action. [Implementation](./src/blocks/task_card.py).
 - **[Video](https://docs.slack.dev/reference/block-kit/blocks/video-block)**: Displays an embedded video player. [Implementation](./src/blocks/video.py).
+
+### Block elements
+
+- **[Attachment mention](https://docs.slack.dev/reference/block-kit/block-elements/attachment-mention-element)**: Renders as a rich app attachment or entity reference. [Implementation](./src/block_elements/attachment_mention.py).

block-kit/src/block_elements/attachment_mention.py

@@ -0,0 +1,26 @@
+from slack_sdk.models.blocks import RichTextBlock
+from slack_sdk.models.blocks.block_elements import (
+    RichTextElementParts,
+    RichTextSectionElement,
+)
+
+
+def example01() -> RichTextBlock:
+    """
+    Renders as a rich app attachment or entity reference.
+    https://docs.slack.dev/reference/block-kit/block-elements/attachment-mention-element/
+
+    An attachment mention referencing an app attachment by URL.
+    """
+    block = RichTextBlock(
+        elements=[
+            RichTextSectionElement(
+                elements=[
+                    RichTextElementParts.AttachmentMention(
+                        url="https://example.com/attachment"
+                    )
+                ]
+            )
+        ]
+    )
+    return block

block-kit/tests/block_elements/test_attachment_mention.py

@@ -0,0 +1,23 @@
+import json
+
+from src.block_elements import attachment_mention
+
+
+def test_example01():
+    block = attachment_mention.example01()
+    actual = block.to_dict()
+    expected = {
+        "type": "rich_text",
+        "elements": [
+            {
+                "type": "rich_text_section",
+                "elements": [
+                    {
+                        "type": "attachment_mention",
+                        "url": "https://example.com/attachment",
+                    }
+                ],
+            }
+        ],
+    }
+    assert json.dumps(actual, sort_keys=True) == json.dumps(expected, sort_keys=True)