Can anybody explain to me what the "Default Namespace" option of a project does/did? (It's there in Delphi 2007 but I can't find it in Delphi 10.1, no idea when it was introduced and when it went away. I have never used it.)

Can anybody explain to me what the "Default Namespace" option of a project does/did? (It's there in Delphi 2007 but I can't find it in Delphi 10.1, no idea when it was introduced and when it went away. I have never used it.)