sourceOrigin property
The browser security origin of the sending document, when available.
A serialized origin includes the scheme, host, and non-default port.
The string "null" represents an opaque origin; Dart null means the
platform could not determine the origin. Neither grants a trusted origin.
This field is never derived solely from sourceUrl, since a document's
URL does not establish its security origin.
Implementation
final String? sourceOrigin;