title: Boost Spirit parser rule to parse square brackets
body: <p>I have to parse a string that can optionally have square brackets in it. For e.g. This can be my token string:</p>
  <p>xyz[aa:bb]:blah</p>
  <p>I have used rules like</p>
  <ul>
  <li>+(~qi::char_(&quot;\r\n;,=&quot;))</li>
  <li>+(~qi::char_(&quot;\r\n;,=&quot;) | &quot;[&quot; | &quot;]&quot;)</li>
  <li>+(qi::char_ - qi::char_(&quot;\r\n;,=&quot;))</li>
  </ul>
  <p>But none of them accepts the square brackets. Is there some special handling of [] in the parser?</p>