C:\>perl -MO=Concise -E"print '1' =~ /^\d$/"
7  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 46 -e:1) v:%,{ ->3
6     <@> print vK ->7
3        <0> pushmark s ->4
5        </> match(/"^\\d$"/) lKS/RTIME ->6
4           <$> const[PV "1"] s ->5