Constant RESOLVE_PORTS 

pub const RESOLVE_PORTS: &str = "DIDBOT_RESOLVE_PORTS";

The environment variable naming which port a loopback hostname’s documents answer on, as host=port pairs separated by commas.

A did:web carries no port, so resolving one means port 443 — and one machine has one port 443. A developer’s own stack takes it (see docs/running-locally.md); a harness starting several servers at once cannot, so it says here where each one is and every tool in this workspace resolves accordingly. A browser is told the same thing through its own resolver rules.

Only a loopback hostname may be named. An entry for anything else is ignored, so this can never move where a real name resolves.