Adjust typings in headings options (#15833)

Other (heading): Adjusted types in heading config options to enable passing the custom heading elements.

packages/ckeditor5-heading/src/headingconfig.ts

@@ -7,7 +7,8 @@
  * @module heading/headingconfig
  */
 
-import type { ViewElementDefinition } from 'ckeditor5/src/engine.js';
+import type { ArrayOrItem } from 'ckeditor5/src/utils.js';
+import type { MatcherPattern, ViewElementDefinition } from 'ckeditor5/src/engine.js';
 
 /**
  * The configuration of the heading feature.
@@ -72,7 +73,7 @@ export interface HeadingConfig {
 /**
  * Heading option descriptor.
  */
-export type HeadingOption = HeadingElementOption | HeadingParagraphOption;
+export type HeadingOption = HeadingElementOption | HeadingParagraphOption | HeadingCustomElementOption;
 
 export interface HeadingElementOption {
 
@@ -100,6 +101,44 @@ export interface HeadingElementOption {
 	 * Icon used by {@link module:heading/headingbuttonsui~HeadingButtonsUI}. It can be omitted when using the default configuration.
 	 */
 	icon?: string;
+
+	/**
+	 * An array with all matched elements that the view-to-model conversion should also accept.
+	 */
+	upcastAlso?: ArrayOrItem<ViewElementDefinition | MatcherPattern>;
+}
+
+export interface HeadingCustomElementOption {
+
+	/**
+	 * Name of the model element to convert.
+	 */
+	model: `heading${ string }`;
+
+	/**
+	 * Definition of a view element to convert from/to.
+	 */
+	view: ViewElementDefinition;
+
+	/**
+	 * The user-readable title of the option.
+	 */
+	title: string;
+
+	/**
+	 * The class which will be added to the dropdown item representing this option.
+	 */
+	class: string;
+
+	/**
+	 * Icon used by {@link module:heading/headingbuttonsui~HeadingButtonsUI}. It can be omitted when using the default configuration.
+	 */
+	icon?: string;
+
+	/**
+	 * An array with all matched elements that the view-to-model conversion should also accept.
+	 */
+	upcastAlso?: ArrayOrItem<ViewElementDefinition | MatcherPattern>;
 }
 
 export interface HeadingParagraphOption {
@@ -123,4 +162,9 @@ export interface HeadingParagraphOption {
 	 * Icon used by {@link module:heading/headingbuttonsui~HeadingButtonsUI}. It can be omitted when using the default configuration.
 	 */
 	icon?: string;
+
+	/**
+	 * An array with all matched elements that the view-to-model conversion should also accept.
+	 */
+	upcastAlso?: ArrayOrItem<ViewElementDefinition | MatcherPattern>;
 }