You can also use the `child` option to include child documents in markdown.

```{r test-main, child='knitr-child.Rmd'}
```

You can continue your main document below, of course.

```{r test-another}
pmax(1:10, 5)
```

If you refer to a child document in a chunk, only the child document will be evaluated. 
Other code in the chunk will not be evaluated when you `render` the document.

```{r test-warning-option, include=FALSE}
options(knitr.child.warning = FALSE)
```

```{r test-warning, child='knitr-child2.Rmd'}
x <- "this code is not evaluated"
x
```