How does role composition work?

http://docs.splunk.com/Documentation/Splunk/6.0/Security/Aboutusersandroles#How_users_inherit_search_filter_restrictions

I read the blurb above, but still find myself with questions.

Not using inheritance, but rather composition.

What would I expect to happen if:

Role A : gives search on index XYZ, with search filter "source=XYZ_App1" Role B : gives search on index XYZ, with search filter "source=XYZ_App2" Role C : gives search on index XYZ, with no search filter Role D : gives search on index 123, with search filter "source=123_test" Role E : gives search on index XYZ, with search filter source=XYZ_App1 ERROR Role F : gives search on index 123, with search filter source=123_test INFO

User1 is assigned Role A and Role B User2 is assigned Role A and Role C User3 is assigned Role A and Role D User4 is assigned Role E and Role F

What will the effective search filter be for these users?

Any advice in the way of gotchas around composing roles?