User Data - Arnold User Guide
It is possible to create arbitrary user data that can be attached to any object. This user data can then later be used at shading time by specific nodes with a user prefix. The convention used to store the user data can be found in different data types such as color and float. For example:
Create an aiUserDataFloat and call it TestFloat:
Export the scene as a .ass file and open it in a text editor. We can see that the float TestFloat is stored in the .ass file as follows:
