docs: private static void bodyWithBuilder(
        SourceBuilder code,
        Datatype datatype,
        Map<Property, PropertyCodeGenerator> generatorsByProperty,
        String typename,
        Predicate<PropertyCodeGenerator> isOptional) {
      Variable result = new Variable("result");
  
      code.add("  %1$s %2$s = new %1$s(\"%3$s{", StringBuilder.class, result, typename);
      boolean midStringLiteral = true;
      boolean midAppends = true;
      boolean prependCommas = false;
  
      PropertyCodeGenerator lastOptionalGenerator = generatorsByProperty.values()
          .stream()
          .filter(isOptional)
          .reduce((first, second) -> second)
          .get();
  
      for (Property property : generatorsByProperty.keySet()) {
        PropertyCodeGenerator generator = generatorsByProperty.get(property);
        if (isOptional.test(generator)) {
          if (midStringLiteral) {
            code.add("\")");
          }
          if (midAppends) {
            code.add(";%n  ");
          }
          code.add("if (");
          if (generator.initialState() == Initially.OPTIONAL) {
            generator.addToStringCondition(code);
          } else {
            code.add("!%s.contains(%s.%s)",
                UNSET_PROPERTIES, datatype.getPropertyEnum(), property.getAllCapsName());
          }
          code.add(") {%n    %s.append(\"", result);
          if (prependCommas) {
            code.add(", ");
          }
          code.add("%s=\").append(%s)", property.getName(), property.getField());
          if (!prependCommas) {
            code.add(".append(\", \")");
          }
          code.add(";%n  }%n  ");
          if (generator.equals(lastOptionalGenerator)) {
            code.add("return %s.append(\"", result);
            midStringLiteral = true;
            midAppends = true;
          } else {
            midStringLiteral = false;
            midAppends = false;
          }
        } else {
          if (!midAppends) {
            code.add("%s", result);
          }
          if (!midStringLiteral) {
            code.add(".append(\"");
          }
          if (prependCommas) {
            code.add(", ");
          }
          code.add("%s=\").append(%s)", property.getName(), (Excerpt) generator::addToStringValue);
          midStringLiteral = false;
          midAppends = true;
          prependCommas = true;
        }
      }
  
      checkState(prependCommas, "Unexpected state at end of toString method");
      checkState(midAppends, "Unexpected state at end of toString method");
      if (!midStringLiteral) {
        code.add(".append(\"");
      }
      code.add("}\").toString();%n", result);
    }