let us say in my application the below are my classes.
let us say I need to have a declare index rule which needs to be run in the primary pages of these classes and the mapping is same.
so i will create declare index rules in each of those classes which will be almost the same except the "source page context class" which will be having values as abc-work-policy, abc-work-policy-auto, abc-work-policy-fire.
if suppose i need to add a new property to be indexed then i need to update all the three index rules which will be pain to maintain.
to overcome the above i have created a declare index rule in abc-work-policy class and i have mentioned the "source page context class" as "Primary" and it is getting fired when instances of abc-work-policy, abc-work-policy-auto, abc-work-policy-fire is getting modified/updated.