my first guess is perlsub#Prototypes

* means only type globs allowed (# hmm ... only partly correct, see below)

; means here everything following the first argument is optional.

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A * allows the subroutine to accept a bareword, constant, scalar expression, typeglob, or a reference to a typeglob in that slot. The value will be available to the subroutine either as a simple scalar, or (in the latter two cases) as a reference to the typeglob.

...

A semicolon (; ) separates mandatory arguments from optional arguments. It is redundant before @ or % , which gobble up everything else.