Using definedness for flow control is one reason why I felt it would be suitable to use in the ternary operator example. I have also seen this used in cgi.pm where the ternary queries if the value is a reference as the method expects and proceeds accordingly.

An example of using undefinedness as a control flow can be seen in this node where I help a fellow monk with identifying and then filling initialised array indexes. Trying to edit HoAoA entries. This does not use ternary condition syntax.

Coyote