Correct 'warranty' itemprop syntax

Question

What syntax is correct for warranty itemprop in https://schema.org/Offer?

This one

<meta itemprop="warranty" content="2ANN" />

or …

<meta itemprop="warranty" content="2 ANN" />

or with hierarchy …

<span itemprop="warranty" itemscope itemtype="https://schema.org/WarrantyPromise">
  <span itemprop="durationOfWarranty" itemscope itemtype="https://schema.org/QuantitativeValue">
    <span itemprop="value">2</span> years
    <meta itemprop="unitCode" content="ANN" />
  </span>
</span>

Answer 1

The warranty property expects a WarrantyPromise as value:

Values expected to be one of these types
WarrantyPromise

So your last example is in line with Schema.org’s model.

(That doesn’t necessarily mean that consumers (e.g., search engines) would not also understand your first examples, but if you don’t have strong reasons against it you should go with the recommended approach.)