backdrop_error_levels in includes/errors.inc

Maps PHP error constants to watchdog severity levels.

dblog_overview in modules/dblog/dblog.admin.inc

Page callback: Displays a listing of database log messages.

DBLogTestCase::getSeverityConstant in modules/dblog/tests/dblog.test

Gets the watchdog severity constant corresponding to the CSS class.

hook_watchdog in modules/system/system.api.php

Log an event message.

system_logging_settings in modules/system/system.admin.inc

Form builder; Configure error reporting settings.

watchdog_severity_levels in includes/common.inc

Returns a list of severity levels, as defined in RFC 3164.