Interface Groups clarification/feature request

[firewalluser]

AMD64 2.2.4
https://doc.pfsense.org/index.php/Interface_Groups

I've setup multiple Interface Groups with interfaces (a unique vlan for each device) that can be found in one or more IG's.

I cant see in the docs what order the IG's are processed in, although it does state after floating rules and before interface rules.
Should I even be using an interface in more than one group?
So far my limited tests suggest it doesnt matter but would like clarification.

Feature Request for IG's, is to have an option to state whether the IG rules are applied edit be_for_e the interface rules or after.