From type/Backtrace

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method next-interesting-index(Backtrace:D: Int $idx = 0, :$named, :$noproto, :$setting)

Returns the index of the next interesting frame, once hidden and other settings are taken into account. $named will decide whether to printed only those with a name, $noproto will hide protos, and $setting will hide those are considered setting.

sub zipi { { { die "Something bad happened" }() }() };
try zipi;
say $!.backtrace.next-interesting-index;           # OUTPUT: «2␤» 
say $!.backtrace.next-interesting-index( :named ); #  OUTPUT: «4␤»