(?<P_ROOTCODE>  ####        The start of a named capturing block (also $1)

  .*            ####          Match any character (except newline), zero-or-more times (as many possible)

)               ####        The end of the named capturing block

(?{ push(@::rc1, ${^MATCH}) })
              ####        Execute a block of code

\K              ####        Pretend the final match starts here

(?{ $::p_rootcode = "@::rc1" })
              ####        Execute a block of code

(?<DAY1>        ####        The start of a named capturing block (also $2)

  [0-9]         ####          Match any of the listed characters

)               ####        The end of the named capturing block

(?{ push(@::rc2, ${^MATCH}) })
              ####        Execute a block of code

\K              ####        Pretend the final match starts here

(?<P_MON_CODE>  ####        The start of a named capturing block (also $3)

  [A-Z]         ####          Match any of the listed characters

)               ####        The end of the named capturing block

(?{ push(@::rc3, ${^MATCH}) })
              ####        Execute a block of code

$               ####        Match only if at end of string (or final newline)