Function scalar 

fn scalar(raw: &str) -> String

One YAML scalar’s value, read from the text after its key.

The scan used to trim().trim_matches(['"', '\'']), which is right for a bare or a quoted value and wrong for a commented one: site_url: https://… # the published base yielded the URL with the comment attached, and D41 bakes that string into policy.site_base and thus into every self-hosted Rust link the moment somebody runs --mode write. Nothing downstream could see it — check-api-links resolves against the rustdoc tree rather than against the site, and an external URL is invisible to mkdocs --strict (§1.3.152). The option is documented in mkdocs.yml today with the comment above the key, which is exactly why the bug was latent: moving it to the end of the line is an ordinary edit.

Two YAML rules, and no more than these two:

• a quoted scalar ends at its closing quote, so a # inside it is data;
• in an unquoted scalar a # opens a comment only when a space or tab precedes it (YAML 1.2 §6.6). A # that does not — the fragment in …/page/#anchor — is part of the value.