Custom attributes in rasa nlu.yml

I want to add few custom attributes with respect to every intent in rasa nlu.yml, but could not find such thing in documentation. Purpose is to further classify intent based on say for a domain or customer.

For example, bookappointment, searchreservations are part of Travel domain, while makepayment, addcredit are of Finance Domain.

How can I maintain such information for respective intents? If not in nlu.yml then which other can be a better place to maintain it?