def find_nestings(fields, prefix):
    """Recursively finds all reusable fields in the fields dictionary."""
    nestings = []
    for field_name, field in fields.items():
        if 'reusable' in field:
            nestings.append(prefix + field_name)
        if 'fields' in field:
            nestings.extend(find_nestings(field['fields'], prefix + field_name + '.'))
    return nestings