Twenty Twenty-One: Add missing documentation for some global variables.

Props sabernhardt, upadalavipul, shailu25, rajinsharwar, audrasjb, viralsampat, noruzzaman, huzaifaalmesbah, SergeyBiryukov.
Fixes #58715.

git-svn-id: https://develop.svn.wordpress.org/trunk@62483 602fd350-edb4-49c9-b593-d223f7449a82

Author: SergeyBiryukov

src/wp-content/themes/twentytwentyone/functions.php

@@ -9,7 +9,11 @@
  * @since Twenty Twenty-One 1.0
  */
 
-// This theme requires WordPress 5.3 or later.
+/**
+ * This theme requires WordPress 5.3 or later.
+ *
+ * @global string $wp_version The WordPress version string.
+ */
 if ( version_compare( $GLOBALS['wp_version'], '5.3', '<' ) ) {
 	require get_template_directory() . '/inc/back-compat.php';
 }

src/wp-content/themes/twentytwentyone/inc/back-compat.php

@@ -31,7 +31,7 @@ function twenty_twenty_one_switch_theme() {
  *
  * @since Twenty Twenty-One 1.0
  *
- * @global string $wp_version WordPress version.
+ * @global string $wp_version The WordPress version string.
  *
  * @return void
  */
@@ -50,7 +50,7 @@ function twenty_twenty_one_upgrade_notice() {
  *
  * @since Twenty Twenty-One 1.0
  *
- * @global string $wp_version WordPress version.
+ * @global string $wp_version The WordPress version string.
  *
  * @return void
  */
@@ -74,7 +74,7 @@ function twenty_twenty_one_customize() {
  *
  * @since Twenty Twenty-One 1.0
  *
- * @global string $wp_version WordPress version.
+ * @global string $wp_version The WordPress version string.
  *
  * @return void
  */