title: Regex to validate strings having only characters (without special characters but with accented characters), blank spaces and numbers
body: <p>I am using Ruby on Rails 3.0.9 and I would like to validate a string that can contain only characters (case insensitive characters), blank spaces and numbers.</p>
  
  <p>More:</p>
  
  <ul>
  <li>special characters <em>are not</em> allowed (eg: !"£$%&amp;/()=?^) except <code>-</code> and <code>_</code>;</li>
  <li>accented characters <em>are</em> allowed (eg: à, è, é, ò, ...);</li>
  </ul>
  
  <p>The regex that I know from <a href="https://stackoverflow.com/questions/6765020/regex-to-validate-string-having-only-characters-not-special-characters-blank-s">this question</a> is <code>^[a-zA-Z\d\s]*$</code> but this do not validate special characters and accented characters.</p>
  
  <p><strong>So, how I should improve the regex?</strong></p>