multipage global variable represents whether the current WordPress post or page to be displayed is multi-paged or not. It is set in the function
setup_postdata($post) defined in [wordpress root folder]/wp-includes/functions.php. A post is broken in multiple pages wherever
<!--nextpage--> is inserted inside the post. pages global variable is used to hold the content of multiple pages of the post.
Theme developers can use the function wp_link_pages($args=”), in [wordpress root folder]/wp-includes/template-functions/post.php, in the WordPress loop to display links to the next and previous pages of the post.
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