title: Does the 'o' modifier for Perl regular expressions still provide any benefit?
body: <p>It used to be considered beneficial to include the 'o' modifier at the end of Perl regular expressions.  The current <a href="http://perldoc.perl.org/" rel="noreferrer">Perl documentation</a> does not even seem to list it, certainly not at the <a href="http://perldoc.perl.org/perlre.html#Modifiers" rel="noreferrer">modifiers section of perlre</a>.</p>
  
  <p>Does it provide any benefit now?</p>
  
  <p>It <em>is</em> still accepted, for reasons of backwards compatibility if nothing else.</p>
  
  <hr>
  
  <p>As noted by J A Faucett and brian d foy, the 'o' modifier is still documented, if you find the right places to look (one of which is not the <code>perlre</code> documentation).  It is mentioned in the <a href="http://perldoc.perl.org/perlop.html#Regexp-Quote-Like-Operators" rel="noreferrer">perlop</a> pages. It is also found in the <a href="http://perldoc.perl.org/perlreref.html" rel="noreferrer">perlreref</a> pages.</p>
  
  <p>As noted by Alan M in the accepted answer, the better modern technique is usually to use the qr// (quoted regex) operator.</p>