constants are subroutines returning (lists of) scalars.

heredocs are plain strings. they just have a different syntax from "normal" quoted strings.

Everything after (and before) __DATA__ / __END__ is in a file, but everything after __DATA__ or __END__ is not processed until read (via the DATA filehandle, or by opening and reading __FILE__), so it's not perl data.

A list differs from an array. I'm not sure if you can call a list a data type, in perl, though.