Hi Al,
There’s currently no support for reflecting on the type of a value in the formula language. With respect to the People type - when you @ref a person what you’re getting back is a reference to a row in a hidden People table. You’ll notice you can access properties on the person reference such as name, email, avatar, etc. We pull this information from the Google Profile when the user logs into the Coda eco-system.
The People table is automatically populated by all “collaborators” of the document - the simple version is this contains all people who’ve accessed the document or had the document directly shared with them (even if they never logged in). These references behave identically to all other refs you might have to your own tables.
Hope that helps,
Nigel.