anchor.diff:      return <code>null</code> to indicate a match failure.</p>
   
       <p>The code inside the action has access to all variables and functions
  -    defined in the initializer at the beginning of the grammar.</p>
  +    defined in the initializer at the beginning of the grammar. Curly braces in
  +    the action code must be balanced.</p>
     </dd>
   
     <dt><code><em>expression<sub>1</sub></em> / <em>expression<sub>2</sub></em> / ... / <em>expression<sub>n</sub></em></code></dt>
  
positive.code:     advance the parser position; otherwise consider the match failed.</p>
  
      <p>The code inside the predicate has access to all variables and functions
      defined in the initializer at the beginning of the grammar.</p>
    </dd>
  
    <dt><code><em>label</em> : <em>expression</em></code></dt>
  
negative.code: JavaScript code in curly braces ("{" and "}"). This code is executed before the
  generated parser starts parsing. All variables and functions defined in the
  initializer are accessible in <a href="#action">rule actions</a> and <a
  href="#semantic-predicate">semantic predicates</a>. Curly braces in the
  initializer code must be balanced.</p>
  
  <p class="center">
    <img src="/img/rule.png" width="742" height="100" alt="PEG.js grammar rule">
  