Writing visitor for url()

[niksy]

In the documentation it says the following:

Visitors can return a new value to update it. Each visitor accepts a different type of value, and usually expects the same type in return. This example multiplies all lengths by 2:

So, if I’m writing visitor for url(), this is what I have:

const visitor = {
  Url({ url, loc }) {
    if (url.includes("foo")) {
      return { loc, url: url.replace("foo", "foofoo") };
    }
  },
};

Is this the right approach for this?
Do I need to do anything with the loc property, or should I just pass it as-is?

I’m asking because I don’t know if this has any relation to other processes after LightningCSS, e.g. source map mappings.