rules expressions documentation

[anshibanov]

First of all, thank you very much for this amazing project.

A big request - could you please provide a little more detailed information on the compilation rules expressions?
I mean:

rules:
  example_rule:
    name: Example Rule
    expression: or (eq .Message.Subject "cam-1") (eq .Message.Subject "cam-2") <---- This is

What variables are available? A few complex examples would be very helpful

[anshibanov]

And is it possible to have a rule for *@script.test where the asterisk is any string?