CA and Named CA is a priority list and will cast spells/cas based on availability and how far up the list they are.
Chain tab is a set casting order that will be followed everytime. It calculates the longest recast spell/ca in the list and will only run the chain once everything is ready to be cast (unless you choose optional for certain spells). It will only hold spells/cas back if the recast of that spell would be longer than the longest spells/cas recast.
Example (Made up numbers):
Assassinate has a 10 minute recast.
Ability A has a 30 second recast.
Ability B has a 3 minute recast.
Ability C has a 5 minute recast.
It runs the chain and casts all four abilities in order from assassinate to ability C. Then as ability A, B, and C become available it will cast them again, but only if the remaining recast time of Assassinate is more than 5 minutes. This would mean that Ability B is going to be cast 3 times (3+3+3 = 9 Minutes) and will be held back for 1 minute while assassinate recast finishes. The it would start the chain all over again.
If I've missed something or have something wrong, I'm sure Kannkor will be around soon.
