{
  // The replacer is called on every value, top-level and nested alike, and
  // its replacement re-enters the conversion in the original's place. A
  // replacer which throws is taken to have declined.
  "/options": {
    replacer: (value) => {
      if (value === 1) return "one";
      if (value === 2) return new Map();
      if (value === 3) throw new Error("no thanks");
      if (value?.whole === true) return "replaced";
      return value;
    },
  },

  "in place": { a: 1, b: 5 },

  "converted, not verbatim": { a: 2 },

  "declined by a throw": { a: 3, m: new Map() },

  "top level": { whole: true, a: 1 },
}

--

in place:
{a:"one",b:5}
{
  a: "one",
  b: 5
}
{
  a: "one",
  b: 5
}

converted, not verbatim:
{a:/Map(...)}
{
  a: /Map(...)
}
{
  a: {
    "/Map": "/..."
  }
}

declined by a throw:
{a:3,m:/Map(...)}
{
  a: 3,
  m: /Map(...)
}
{
  a: 3,
  m: {
    "/Map": "/..."
  }
}

top level:
"replaced"
"replaced"
"replaced"