title: Exact usage for hidden indent option with knitr
body: <p>I'm trying to render rmarkdown to markdown and implement the example for the hidden indentation option from <a href="http://yihui.name/knitr/options/" rel="nofollow">Yihui Xie's</a> documentation for knitr: </p>
  
  <blockquote>
    <p>There is a hidden option indent which stores the possible leading white spaces of the chunk, e.g. for the chunk below, indent is a character string of two spaces:</p>
  </blockquote>
  
  <pre><code>  ```{r}
    rnorm(10)
    ```
  </code></pre>
  
  <p>Which I interpret to mean simply add two spaces before each line in the code as I entered above. However, when I knit the document the code block is not recognized because of the leading spaces. Obviously I am not understanding the correct way to implement this option.</p>
  
  <p>I want to do this because I'm writing a book with <a href="https://leanpub.com/" rel="nofollow">Leanpub</a> and I need to render rmarkdown to markdown. The default four spaces leads to a code block with Leanpub's markdown interpreter, but doesn't put code and output in nice boxes the way rmarkdown/knitr users are used to. If I can control the whitespace in markdown, I will have more control over how my code and output looks. If they took html files as a normal part of their workflow it would be easy, but this is not fully supported. </p>