Function substitute_references_if_needed_and_apply 

pub fn substitute_references_if_needed_and_apply(
    name: &Name,
    kind: SubstitutionFunctionKind,
    value: &Arc<VariableValue>,
    stylist: &Stylist,
    context: &mut Context<'_>,
    attribute_tracker: &mut AttributeTracker<'_>,
)

Replace var(), env(), and attr() functions in a pre-existing variable value.