Document non-enumerable properties
![image](https://user-images.githubusercontent.com/2700528/50730264-1d156a80-1141-11e9-9f25-786df4d96b0f.png)

will this line actually work? as far as I can tell, a layer has no valid method for `sharedStyle`, and you just have to get the `sharedStyleId` and then look it up yourself?