What is the difference between context of "sighup", "super-backend", and "backend" in pg_settings?

[周书林 <zhoushulin1992@xxxxxxxxx>]

Hi, 

I am interested in the configuration parameter of Postgres. I found that the configuration parameters in context of "sighup", "super-backend", and "backend" are all required to send "SIGHUP" signal to postmaster for rereading configuration files. So my question is, what is the difference between them, except for the super-usre privilege requirment  between  "super-backend", and "backend"?

Sincerely,

Shulin