FhirPath: Definition of environment variables

[YanBos]

Hello everyone,

I was wondering on how to use variables defined through the variable extension inside a questionnaire. I tried to access the variable sevenDaysFromNow within the following example:

var questionnaire = new Questionnaire
{
    Name = "Questionnaire",
    Item = new()
    {
        new Questionnaire.ItemComponent
        {
            Text = "Question 1",
            LinkId = "1",
            Item = new()
            {
                new Questionnaire.ItemComponent
                {
                    Text = "Question 1.1",
                    LinkId = "1.1",
                }
            }
        }
    },
    Extension = new List<Extension> 
    {
        new Extension 
        {
            Url = "http://hl7.org/fhir/StructureDefinition/variable",
            Value = new Expression 
            {
                Name = "sevenDaysFromNow",
                Language = "text/fhirpath",
                Expression_ = "today() + 7"
            }
        }
    }
};

Is it possible to somehow use the variable %sevenDaysFromNow in an Expression or if not is it possible to define it? Any help would be appreciated :)

Thanks in advance!

Kind regards