admin_bar_links_alert in modules/admin_bar/admin_bar.inc

Build alert indicator.

backdrop_check_module in includes/install.inc

Checks a module's requirements.

drupal_requirements_severity in includes/drupal.inc

Extracts the highest severity from the requirements array.

install_verify_requirements in includes/install.core.inc

Verifies the requirements for installing Backdrop.

system_status in modules/system/system.admin.inc

Menu callback: displays the site status report. Can also be used as a pure check.

update_check_requirements in ./update.php

Checks update requirements and reports errors and (optionally) warnings.