title: Where are the values of this variable coming from? Doesn't seemed to be defined anywhere
body: <p>I am new to Rstudio and I'm trying to learn how to use R Markdown. When I create a new R Markdown file, I am greeted with the following default document. </p>
  
  <p><img src="https://i.stack.imgur.com/HH0MY.png" alt=""></p>
  
  <p>Note how I've specifically assigned the 'cars' variable a NULL value, yet when running it cars becomes a data frame populated with values. Given that there is no assignment anywhere within the document or any variables present in the environment, it really bothers me not know the source for those values.</p>
  
  <p>I would greatly appreciate knowing how the cars dataframes comes to be from apparently spontaneously.</p>