FhirPath
It is even possible to integrate FHIR path when you create examples. You can use FHIR path in any value by enclosing it with << >>.
For example:
Patient:
id: john
name.given: <<id.upper()>>
will produce:
{
"resourceType": "Patient",
"id": "john",
"name": [
{
"given": [
"JOHN"
]
}
]
}