r is backquoted version of it is one of <tt>" ' % \ \n \r \t</tt>
 .
 
 A string is enclosed within single quotes if a character has been
 backquoted using the previous rule above or contains <tt>{ }</tt> or is
 exactly equal to the strings <tt>, ? space or ""</tt> (empty string).
 
 A quoted question mark distinguishes it from the missing value which is
 represented as an unquoted question mark in arff files.</div>
<dl><dt><span class="strong">Parameters:</span></dt><dd><code>string</code> - the string to 