title: Extract first sentence in string
body: <p>I want to extract the first sentence from following with regex. The rule I want to implement (which I know won't be universal solution) is to extract from string start <code>^</code> up to (including) <strong>the first period/exclamation/question mark that is preceded by a lowercase letter or number</strong>.</p>
  
  <pre><code>require(stringr)
  
  x = "Bali bombings: U.S. President George W. Bush amongst many others has condemned the perpetrators of the Bali car bombing of October 11. The death toll has now risen to at least 187."
  </code></pre>
  
  <p>My best guess so far has been to try and implement a non-greedy <a href="https://stackoverflow.com/a/7124976/1156245">string-before-match approach</a> fails in this case:</p>
  
  <pre><code>str_extract(x, '.+?(?=[a-z0-9][.?!] )')
  [1] NA
  </code></pre>
  
  <p>Any tips much appreciated.</p>