Required? Doesn't [] mean optional?

And it's part of Sybase::DBlib, because that's what the DBlib C-Client libraries support. You're required to use pass a pointer to a LOGINREC when using dbopen to establish a connection. The LOGINREC contains a mandatory DBSETLPWD (password) record, and optional DBSETLUSER (user), DBSETLHOST (host) and DBSETAPP (application) records.

Sybase::DBlib::new does all the C stuff for you, but doesn't rob you of options. Hence, the optional $appname.