I've mistakenly said the feature became experimental in 5.18 in the past too. But while the experimental warnings were added in 5.18, it was flagged as experimental in 5.16.

Quote 5.16's perlsyn,

you can say use feature "switch"; to enable an experimental switch feature.

Also,

Under the "switch" feature, Perl gains the experimental keywords given, when, default, continue, and break.

Added break, default and continue to the table.

In reply to Re^2: Perl named operator and builtin subs introduced since 5.6 by ikegami
in thread Finding when a feature or keyword was introduced by Bod

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