Default Property

A default property is a field the analytics library attaches to every event automatically, such as page address, referrer, device type and time.

The values are read from the runtime environment at send time and differ by platform: a web library carries the address and referrer, a mobile library carries app version and device model. They differ from super properties, which you register yourself so they attach to later events, because default properties belong to the library itself. The common mistake is treating these fields as certain: the referrer is empty on direct visits and in many in-app webviews, and device type is inferred from the user agent string, so a spoofed or unknown agent yields a wrong value with no error raised.