multi entry in shopper custom field

[ydl]

We need to create a "multi-entries" of a shopper custom "complex" field.

We want to ask to user to enter all of it "pets". each pet has the following attributes: "type" (dog, cat etc.), name, age, weight etc.
We assume some of the customer will have nore than one pet.

Any idea how to define the shopper custom filed to support it?
Is it possible?

If not, can someone point out a tutorial about writing a shopper custom field extension (I didn't find such a document)

[balai]

where this custom field will be field in?
In which page?

[ydl]

in user profile.

on of the solution which I check is to write a userfield  plugin