Man pages matching name moosex::setonce in section 3pm:

MooseX::SetOnce.3pm.en	debian 10 / libmoosex-setonce-perl
MooseX::SetOnce.3pm.en	debian 11 / libmoosex-setonce-perl
MooseX::SetOnce.3pm.en	debian 12 / libmoosex-setonce-perl