What Business Rule processes Assignment Rules

[G24]

Hello smart people.

What Business Rule (?) processes the Assignment Rules in table sysrule_assignment ?

I see the documentation here , but that is not telling me how these magically work.

Are these rules really run any time a user opens an associated record?

Thanks.

[SanjivMeher]

I think there used to be business rule as below, but I can't find it in my personal dev instance. May be part of an update set.