Is there any way to access temporary attachment filenames via Behaviours?

[William Lupton]

I think that the answer to this question is probably "no", because I think I'd need the form token and this link (from the ScriptRunner docs) says that it's not available in REST contexts.

But just possibly Behaviours might be able to get the temporary attachment filenames directly from the form? Unfortunately the "Attachment" field (which is displayed in the form) doesn't seem to be accessible via Behaviours, and I don't really know what else to try.

Background: this is a validator, and the validator function processes the temporary attachments (this works fine). But I'm looking into using Behaviours to allow a preview of what will happen when the transition is allowed to proceed.

[William Lupton]

Clarification: It's wrong to say "it's a validator". It's a transition screen, and there's a validator associated with the transition. I'm looking to use Behaviours before the validator has been invoked.