Consider using SecurityPolicyViolationEvent.sourceFile a USVString

[emilio]

It's a path and generally USVString is used for those. WebKit already does this FWIW.

This is I think only observable if you create a custom event with an unpaired surrogate in the init dictionary (in which case you'd start getting a replacement character rather than the unpaired surrogate).

cc @smaug----

[emilio]

Same for the URI members too I guess