title: What is '?-mix' in a Ruby Regular Expression
body: <p>Just trying to debug a regular expression in ruby. When I print the contents of a regular expression, it shows <code>?-mix</code> at the beginning of the regular expression even though those characters were not part of the expression. Please see the following IRB output to see this illustrated</p>
  
  <pre><code>irb(main):028:0* EXPR = /^a$/
  =&gt; /^a$/
  irb(main):029:0&gt; EXPR
  =&gt; /^a$/
  irb(main):030:0&gt; puts EXPR
  (?-mix:^a$)
  =&gt; nil
  </code></pre>
  
  <p>As you can see, when you use <code>puts</code> to print out the contents of a regular expression, there is <code>?-mix</code> at the beginning. Should I be concerned by this? Where is it coming from? </p>