[New Feature] Option sets

Hi, @cal, trying out option sets, great feature, if i’m understanding it right, it’s like a “list” in excel where you save somewhere in the document for access later.
According to Advice: Auto-populating List, I’m assuming the app users can add/remove a field in data types, they cannot do it to option sets?

For instance, in an expenses app where there are default values but each user would have the freedom to preset & configure their categories with items, e.g.
Category: Transportation
Item: Taxi, Subway, Bus… etc.

Do I create the default values in Data Types instead of Option Sets?
And how do I make the items relative to the categories so that when they select Transportation, they don’t see options like Sandwich or Shoes?

Much appreciate it.