title: codeigniter alpha_numeric form validation not accepting space
body: <p>i want to set form validation so that user cannot add special characters like $, @, &amp;, etc... only alpha numeric characters are allow</p>
  
  <pre><code>$this-&gt;form_validation-&gt;set_rules('cat_name', 'Category Name', 'trim|xss_clean|required|is_unique[cht_category.cat_name]|min_length[5]|max_length[75]|alpha_numeric');
  </code></pre>
  
  <p>when i add category name with space then i get following error
  "The Category Name field may only contain alpha-numeric characters."
  when i add category name without space or single word then its working fine</p>