Question re rustdoc reproducibility

[smoelius]

When I run cargo rustdoc -- -Z unstable-options --output-format=json on the standard library on an Ubuntu machine, I get the same JSON file each time. This has held regardless of whether I run the command locally or on GitHub's ubuntu-latest runner.

If I add --target x86_64-unknown-linux-gnu and run the command on GitHub's macos-latest runner, I get a slightly different file.

Is this expected?

Generally speaking, what is required to ensure reproducibility of cargo rustdoc's JSON output?

Thank you in advance, and sorry if this is not the right place to ask these questions.