install_check_requirements in drupal-6.x/install.php

Check installation requirements and report any errors.

system_requirements in drupal-6.x/modules/system/system.install

Implementation of hook_requirements().

theme_status_report in drupal-6.x/modules/system/system.admin.inc

Theme requirements status report.

unicode_requirements in drupal-6.x/includes/unicode.inc

Return Unicode library status and errors.

update_help in drupal-6.x/modules/update/update.module

Implementation of hook_help().

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