docs: private String simpleElement(StructureDefinition sd, ElementDefinition ed, String typ) {
      String addldef = "";
      ElementDefinition.ElementDefinitionBindingComponent binding = ed.getBinding();
      if(binding.hasStrength() && binding.getStrength() == Enumerations.BindingStrength.REQUIRED && "code".equals(typ)) {
        ValueSet vs = resolveBindingReference(sd, binding.getValueSet());
        if (vs != null) {
          addldef = tmplt(VALUESET_DEFN_TEMPLATE).add("vsn", vsprefix(vs.getUrl())).render();
          required_value_sets.add(vs);
        }
      }
      // TODO: check whether value sets and fixed are mutually exclusive
      if(ed.hasFixed()) {
        addldef = tmplt(FIXED_VALUE_TEMPLATE).add("val", ed.getFixed().primitiveValue()).render();
      }
      return tmplt(SIMPLE_ELEMENT_DEFN_TEMPLATE).add("typ", typ).add("vsdef", addldef).render();
    }