Why is the generic expecting 3 options, although there is only one generic prop?

import { type, scope } from "arktype";

const types = scope({
  queryValue: "null | string | number | bigint | boolean",
  queryValueObject: {
    "[string]": "queryValue",
  },

  "namedDocument<metadata extends queryValueObject = Record<string, never>>": { // namedDocument has only one generic "metadata"
    "data?": "metadata",
  },
}).export();

// this requires 3 options, but I would expect only 1 (metadata)
const namedDocument = types.namedDocument("object", "object", "object")

import { type, scope } from "arktype";

const types = scope({
  queryValue: "null | string | number | bigint | boolean",
  queryValueObject: {
    "[string]": "queryValue",
  },

  "namedDocument<metadata extends queryValueObject = Record<string, never>>": { // namedDocument has only one generic "metadata"
    "data?": "metadata",
  },
}).export();

// this requires 3 options, but I would expect only 1 (metadata)
const namedDocument = types.namedDocument("object", "object", "object")