title: How to skip error checking at Rmarkdown compiling?
body: <p>I was writing an Rmarkdown document (compile to HTML) in RStudio, and there are some code chunks that deliberately generate errors. for example:</p>
  
  <pre><code>```{r}
  sum(a)
  ```
  </code></pre>
  
  <p>Since there is no previous definition for <code>a</code> this chunk will naturally generate an error message like <code>object 'a' not found</code>. I'd like this error message displayed in the final HTML file, but when I press <code>Ctrl+Shift+K</code> in RStudio to "Knit HTML", the compiler reported the error and stopped knitting.</p>
  
  <p>So how can I tell <code>knitr</code> to ignore such error at compiling time and display it in the knitted HTML document?</p>