wp-includes/class-wp-customize-nav-menus.php:1263Prints the markup for available menu item custom links.
protected function print_custom_links_available_menu_item() { ?> <div id="new-custom-menu-item" class="accordion-section"> <h4 class="accordion-section-title"> <button type="button" class="accordion-trigger" aria-expanded="false" aria-controls="new-custom-menu-item-content"> <?php _e( 'Custom Links' ); ?> <span class="toggle-indicator" aria-hidden="true"></span> </button> </h4> <div class="accordion-section-content customlinkdiv" id="new-custom-menu-item-content"> <input type="hidden" value="custom" id="custom-menu-item-type" name="menu-item[-1][menu-item-type]" /> <p id="menu-item-url-wrap" class="wp-clearfix"> <label class="howto" for="custom-menu-item-url"><?php _e( 'URL' ); ?></label> <input id="custom-menu-item-url" name="menu-item[-1][menu-item-url]" type="text" class="code menu-item-textbox" placeholder="https://"> <span id="custom-url-error" class="error-message" style="display: none;"><?php _e( 'Please provide a valid link.' ); ?></span> </p> <p id="menu-item-name-wrap" class="wp-clearfix"> <label class="howto" for="custom-menu-item-name"><?php _e( 'Link Text' ); ?></label> <input id="custom-menu-item-name" name="menu-item[-1][menu-item-title]" type="text" class="regular-text menu-item-textbox"> <span id="custom-name-error" class="error-message" style="display: none;"><?php _e( 'The link text cannot be empty.' ); ?></span> </p> <p class="button-controls"> <span class="add-to-menu"> <input type="submit" class="button submit-add-to-menu right" value="<?php esc_attr_e( 'Add to Menu' ); ?>" name="add-custom-menu-item" id="custom-menu-item-submit"> <span class="spinner"></span> </span> </p> </div> </div> <?php }Introduced in 4.7.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/class-wp-customize-nav-menus.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.