php在函數外宣言global變數有什麼用

php在函數外聲明global變數有什麼用？
php在函數外聲明global變數有什麼用？

我看wordpress的wp-settings.php檔案中有這麼一段：

/*
 * These can't be directly globalized in version.php. When updating,
 * we're including version.php from another install and don't want
 * these values to be overridden if already set.
 */
global $wp_version, $wp_db_version, $tinymce_version, $required_php_version, $required_mysql_version;
require( ABSPATH . WPINC . '/version.php' );

不懂，求解釋，謝謝啦 ^_^沒有作用
並且在 wp-settings.php 中也沒有看到
global $wp_version, $wp_db_version, $tinymce_version, $required_php_version, $required_mysql_version;
只有
require( ABSPATH . WPINC . '/version.php' );沒作用

