domain_categories
Returns the categories currently configured on the domain. Useful primarily
for metadata transformation and validation expressions. Note that the value
returned is cached for a period of time, so if you update your domain's categories,
that change may not be reflected immediately from this function.
Examples:
-- All the domain's categories
domain_categories()
-- Result: {"json":["government","education","business","personal","fun"]}
-- Test if a value exists in the configured categories
json_array_contains(domain_categories(), "education")
-- Result: true
-- Test if a value exists in the configured categories
json_array_contains(domain_categories(), "not actually a category")
-- Result: false
-> json