code: private IndexOf resolveIndexOf(FunctionRef fun) {
          checkNumberOfOperands(fun, 2);
          final IndexOf indexOf = of.createIndexOf();
          indexOf.setSource(fun.getOperand().get(0));
          indexOf.setElement(fun.getOperand().get(1));
          builder.resolveCall("System", "IndexOf", new IndexOfInvocation(indexOf));
          return indexOf;
      }
docs: List Function Support