Add documentation and schema for contentRole block support

Author: t-hamano

docs/reference-guides/block-api/block-supports.md

@@ -608,6 +608,22 @@ When the block declares support for `color.text`, the attributes definition is e
     }
     ```
 
+### contentRole
+
+_**Note:** Since WordPress 6.9._
+
+-   Type: `boolean`
+-   Default value: `true`
+
+This value signals that a block contains user-editable content. When set to true, the block is considered a content block. Content blocks remain editable even when their parent container has content-only locking applied.
+
+```js
+supports: {
+	// Declare support for content role.
+	contentRole: true
+}
+```
+
 ## customClassName
 
 -   Type: `boolean`

schemas/json/block.json

@@ -650,6 +650,11 @@
 					"description": "This property indicates whether the block can split when the Enter key is pressed or when blocks are pasted.",
 					"type": "boolean",
 					"default": false
+				},
+				"contentRole": {
+					"description": "This value signals that a block contains user-editable content. When set to true, the block is considered a content block. Content blocks remain editable even when their parent container has content-only locking applied.",
+					"type": "boolean",
+					"default": false
 				}
 			},
 			"additionalProperties": true