Docs: fix error reference in documentation.
@@ -140,7 +140,7 @@ export default class Schema {
* {@link #register registered} yet.
*
* @param itemName The name of the model element which is being extended.
- * @error schema-cannot-register-item-twice
+ * @error schema-cannot-extend-missing-item
*/
throw new CKEditorError( 'schema-cannot-extend-missing-item: Cannot extend an item which was not registered yet.', this, {
itemName