title: [0-9]+.txt doesn't seem to be matching text files with numeric names
body: <p>This pattern doesn't appear to be correctly matching txt files with numeric names: <code>[0-9]+.txt</code>. <br/>Can someone advise me as to what I'm doing wrong?</p>
  
  <p>Context: <code>$posts = preg_grep("[0-9]+.txt", glob('posts/*.txt'));</code></p>