title: preg_replace of "Word" in a sentence and "Word." on the end of a sentence
body: <p>i want to preg_replace "Word" in PHP. </p>
  
  <pre><code>    $ret = 'I gave my Word to you.';    
      $pattern = '/\bWord\b/i';
      $ret = preg_replace($pattern,"Heart",$ret);
  // echo $ret; = "I gave my Heart to you";
  </code></pre>
  
  <p>This works so far. But if the sentence is "I gave you my Word." or "I gave you my Word!" it doesn't change the "Word." into "Heart."</p>