constant REQUIREMENT_WARNING

backdrop_requirements_url in includes/install.inc

Returns a URL for proceeding to the next page after a requirements problem.

ckeditor_requirements in modules/ckeditor/ckeditor.install

Implements hook_requirements().

image_requirements in modules/image/image.install

Implements hook_requirements() to check the PHP GD Library.

install_verify_requirements in includes/install.core.inc

Verifies the requirements for installing Backdrop.

system_requirements in modules/system/system.install

Implements hook_requirements().

... See full list