docs updates

Author: guybedford

doc/api/modules.md

@@ -233,14 +233,14 @@ by tools converting ES modules into CommonJS modules, following existing ecosyst
 conventions. Code authored directly in CommonJS should avoid depending on it.
 
 To create an ESM module that should provide an arbitrary value to CommonJS, the
-`__cjsUnwrapDefault: true` marker can be used instead:
+`cjsUnwrapDefault: true` marker can be used instead:
 
 ```mjs
 // point.mjs
 export default class Point {
   constructor(c, x) { this.x = x; this.y = y; }
 }
-export const __cjsUnwrapDefault = true;
+export const cjsUnwrapDefault = true;
 ```
 
 ```cjs
@@ -249,6 +249,9 @@ console.log(point);
 // [class Point]
 ```
 
+When using `cjsUnwrapDefault`, no named exports other than the `default` export
+will be accessible to CommonJS importers.
+
 If the module being `require()`'d contains top-level `await`, or the module
 graph it `import`s contains top-level `await`,
 [`ERR_REQUIRE_ASYNC_MODULE`][] will be thrown. In this case, users should