What pattern does "Fail Build on Error Message" use to detect errors

The doc at Build Failure Conditions | TeamCity On-Premises (jetbrains.com) unfortunately doesn't describe exactly what strings/regex Teamcity looks for to decide it's found an error message.

We're sometimes getting spurious build failures where teamcity has spotted a string containing "error" but it's not actually a message we'd like to treat as fatal. If possible I'd like to know exactly what teamcity is using to decide this so I can avoid logging such messages from our build.