title: Regex to match after string before space using RE2
body: <p>I am new to RE2 syntax regex, I want to match first word comes after specific string.</p>
  
  <p>For example:</p>
  
  <p><code><em>java.lang.<strong>OutOfMemoryError</strong>: Java heap space
    Error sending periodic event</em>
  <em>java.lang.<strong>NullPointerException</strong>: Java heap space
    Error sending periodic event</em>
  </code></p>
  
  <p>I want to capture anything comes after <code>java.lang.</code> so I can get <code>OutOfMemoryError</code>, <code>NullPointerException</code> errors. I know in Python and PCRE we can do this using positive lookbehind and regex will be - <code>(?&lt;=java.lang.).*?(?=\s)</code>, but this is not working for RE2.</p>