title: PHP: is there an isLetter() function or equivalent?
body: <p>I am no PHP expert. I am looking for the PHP equivalent of <a href="http://docs.oracle.com/javase/6/docs/api/java/lang/Character.html#isLetter%28char%29" rel="noreferrer">isLetter()</a> in Java, but I can't find it. Does it exist?</p>
  
  <p>I need to extract letters from a given string and make them lower case, for example: "Ap.ér4i5T i6f;" should give "apéritif'. So, yes, there are accentuated characters in my strings.</p>