Add JSDoc block for getSectionRootClientId in block editor package (#…

…65219)

* Add JSDoc block for getSectionRootClientId in block editor

* Apply suggestions from code review

Co-authored-by: Dave Smith <getdavemail@gmail.com>

---------

Co-authored-by: Dave Smith <getdavemail@gmail.com>

packages/block-editor/src/store/private-selectors.js

@@ -548,6 +548,15 @@ export function isZoomOutMode( state ) {
 	return state.editorMode === 'zoom-out';
 }
 
+/**
+ * Retrieves the client ID of the block which contains the blocks
+ * acting as "sections" in the editor. This is typically the "main content"
+ * of the template/post.
+ *
+ * @param {Object} state Editor state.
+ *
+ * @return {string|undefined} The section root client ID or undefined if not set.
+ */
 export function getSectionRootClientId( state ) {
 	return state.settings?.[ sectionRootClientIdKey ];
 }