Clarification on DSL Step Input Binding and Expression Language Support

I'm working with workflow-core's JSON DSL, and I have a few questions regarding step input bindings:

1. Is it strictly WorkflowData property mapping or is there a broader set of supported expressions?

From testing, it seems like expressions like the ternary operator work?

```json
{
"Id": "UpdateStatus",
"Name": "Update Status",
"StepType": "Test.UpdateFGStatusStep, Test",
"Inputs": {
"MessageId": "data.MessageId",
"Status": "data.Status == \"approved\" ? \"sent\" : data.Status"
}
}
```

2. Are there any official docs or guidelines on what is allowed (property binding, static values, nested properties, etc.) inside the Inputs section of a step definition?