title: Repeating large elements in a regular expression
body: <p>I have the following regular expression:</p>
  
  <pre><code>_parser = re.compile('''
                      (?P&lt;a&gt;-?[0-9]+(\.[0-9]+)?(/-?[0-9]+(\.[0-9]+)?)?)?x[+\-]
                      (?P&lt;b&gt;-?[0-9]+(\.[0-9]+)?(/-?[0-9]+(\.[0-9]+)?)?)?y[+\-]
                      (?P&lt;c&gt;-?[0-9]+(\.[0-9]+)?(/-?[0-9]+(\.[0-9]+)?)?)?=0
                      ''', re.VERBOSE)
  </code></pre>
  
  <p>This quite obviously has a lot of repetition in it, so it got me wondering, what's the syntax (if it exists) to repeat blocks of similar expressions in a single expression?</p>