Certain arguments and properties in the extension IDL bindings may be length limited. A concrete example of this is the `notificationId` argument for notifications:

https://cs.chromium.org/chromium/src/chrome/common/extensions/api/notifications.idl?q=notifications.idl&sq=package:chromium&dr&l=150

This is implemented by checking the length in C++ and throwing an error message manually. Because this is implicit, it needs to be duplicated in the API's documentation.

It would be convenient if it could be defined as:

    [MaxLength=500] optional DOMString notificationId

Which could automatically generate the limitation code, provide consistent error messages and power the documentation view.