title: PHP filter using preg_replace to allow only alphanumerics and some punctuation
body: <p>I have a little problem with <code>preg_replace</code>.</p>
  <p>I need a function that removes all characters except <code>[A-z][0-9]</code> and <code>.!?</code>.</p>
  <p>I could use <code>preg_match</code>, but this only verifies the string, and I want to remove the characters.</p>
  <p>This is so I don't end up putting junk characters like <code>&lt;p&gt;</code> and <code>;[[;[p;[</code>
  in the description META tag.</p>
  <p>So the function must do this:</p>
  <p><code>;&quot;)&lt;br&gt;kk23?!</code> → <code>brkk23?!</code></p>
  <p>Any help would be appreciated :D</p>