Attributes on RKVST Assets are extremely flexible and can be (almost!) anything. They do not need to be pre-registered or defined up-front: instead they work like hashtags on social media, being added and tracked from the first time they're seen.
Attributes prefixed with 'arc_' are a little different. This indicates that they are understood by the RKVST platform and may be interpreted in various places (back end services, UI) to provide enhanced functionality. An overview of this is provided in our main concept documentation.