Function check

packages/zod/src/v4/classic/schemas.ts:256–269

(...chks)

  // shared underlying function references across all instances.
  _installLazyMethods(inst, "ZodType", {
    check(...chks) {
      const def = this.def;
      return this.clone(
        util.mergeDefs(def, {
          checks: [
            ...(def.checks ?? []),
            ...chks.map((ch) =>
              typeof ch === "function" ? { _zod: { check: ch, def: { check: "custom" }, onattach: [] } } : ch
            ),
          ],
        }),
        { parent: true }
      );
    },
    with(...chks) {
      return this.check(...chks);
    },