files in /etc/ are global /hoem/you/.blahrc are user specific details.
typically the per user config file will be looked for, and if that fails then try /etc/ then fall back to a hard coded set, or fail completely. this is just a general guide.. not ppossible to set anything like that in stone.
as for the format, it's whatever that author wants. there are no real standards in place, as it's very seldom justifiable or useful.