code: public NumberExpression<Integer> indexOf(Expression<String> str, int i) {
          return Expressions.numberOperation(Integer.class, Ops.INDEX_OF_2ARGS, mixin, str, ConstantImpl.create(i));
      }
docs: Create a {@code this.indexOf(str)} expression
  
  <p>Get the index of the given substring in this String, starting from the given index</p>
  
  @param str string
  @param i zero based index
  @return this.indexOf(str)