Overlapping absence restriction

Summary

How do we restrict 2 absence types not filed on the same day?

Content

We got to setup similar absences for 2 clients but encountered different messages when 2 absence types were filed on the same day. For Client A, an error message was displayed that did not allow the user to submit the absence. For Client B, a warning message was encountered that after selecting OK the absence request was permitted by the system. Where do we control overlapping leaves to facilitate the process of Client A?