Note on User IDs
There are some system tags and other similar places where user ID is present. Examples:
user/1005921515/label/Testinguser/1005921515/state/com.google/rootuser/1005921515/state/com.google/read
When you need to pass those back to the API, you can safely replace the user ID with -. This way you don't have to worry about parametrizing your request parameters.
For example user/1005921515/label/Testing becomes user/-/label/Testing.