The detailed description of shell job control (particularly, for the format, in which job IDs are specified) has been missed for years.
I adopted the POSIX standard text, describing shell job control (https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap03.html#tag_03_203), tried to make it more easy-to-read and also made some small changes according to the actual sh(1) implementation in FreeBSD.
I'm not very experienced with mdoc(7) and this is my first more-or-less big patch, so I will be very happy if you point out my mistakes.
PR: 206284