function chars_restantes(theform) {
  var coment_obj = theform.COMENT_TEXTO;
  var div_numchars = document.getElementById('numchars');

  var chars_restantes = LIMIT_CHARS - coment_obj.value.length;


  if (chars_restantes >= 0) {
    div_numchars.innerHTML = chars_restantes + '';
  }
  else {
    div_numchars.innerHTML = '0';
    coment_obj.value = coment_obj.value.substring(0, LIMIT_CHARS);
    alert('El número máximo de caracteres permitidos es ' + LIMIT_CHARS);
  };
};