From type/Backtrace

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method concise(Backtrace:D:)

Returns a concise string representation of the backtrace, filtered by !.is-hidden && .is-routine && !.is-setting.

This program:

sub inner { say Backtrace.new.concise }
sub outer { inner; }
outer;

results in:

in sub inner at test.p6 line 1
in sub outer at test.p6 line 2