Q:

Is it possible to create a code block of pseudocode in R Markdown/knitr?

I've tried using backticks and tildes, but they require languages. I just want a formatted code block of plain text with highlighted background.
Using eval=FALSE and tidy=FALSE works until reaching a keyword such as if, the subsequent code will be color highlighted in both the .Rmd file and the output PDF. Not specifying a language through the options removes the capability of background highlighting the code in the output.
```{r, eval=FALSE,tidy=FALSE}
loop through each species
    loop through each measurement of the current species
         if measurement ...
etc.
```

A:

Here's some sample code that renders to HTML just fine. It also renders correctly to Word and PDF.
---
title: "Untitled"
output: html_document
---

Here is some plain text.

Next, let's write some pseudo code.  Note that you don't _have_ to specify a language if using plain backticks.

```
object <- [some kind of calculation]
```

If you set `eval = FALSE` you can get the highlighted background

```{r, eval = FALSE}
object <- [some kind of calculation]
Note that this; is not valid R code
```

You may find it interesting that your example works just fine for me.

```{r, eval=FALSE}
loop through each species
    loop through each measurement of the current species
    ...
etc.
```

