This example is accessing the sub-elements of the tag builtin/structure1. Because the elements within a block with a parent class have a child class in addition to the pb_toggle or pb_momentary class, they automatically prepend the parent tag to the tag they are configured for.
This tag accesses "builtin/structure1/sub1"
And this button changes it from 12 to 34 when pressed

This indicator shows the status of "builtin/structure/sub1"

And these buttons change it