title: Are double "" and single '' quotes (always) interchangeable in R?
body: <p>This is perhaps rather a minor question...</p>
  
  <p>but just a moment ago I was looking through some code I had written and noticed that I tend to just use <code>="something"</code> and <code>='something_else'</code> completely interchangeably, often in the same function.</p>
  
  <p>So my question is: Is there R code in which using one or other (single or double quotes) has different behaviour? Or are they totally synonymous?</p>