title: Understanding Positive Look Ahead Assertion
body: <p><a href="https://docs.python.org/3.4/howto/regex.html#lookahead-assertions" rel="nofollow noreferrer">From Python 3.4.1 docs:</a></p>
  <blockquote>
  <p>(?=...)</p>
  <p>Positive lookahead assertion. This succeeds if the contained regular expression, represented here by ..., successfully matches at the current location, and fails otherwise. But, once the contained expression has been tried, the matching engine <strong>doesn’t advance</strong> at all; the rest of the pattern is tried <strong>right where the assertion started</strong>.</p>
  </blockquote>
  <p>I'm trying to understand regex in Python. Could you please help me understand the second sentences, especially the bolded words? Any example will be appreciated.</p>