[aw1621107]

Yes, it's a Compiler Explorer feature. URL includes get rewritten client-side to work as if they were additional files supplied by the user. PR adding the current behavior is at [0], while I think the downloading code itself is at [1].

[0]: https://github.com/compiler-explorer/compiler-explorer/pull/...

[1]: https://github.com/compiler-explorer/compiler-explorer/blob/...