function StripSpacesFromEnds(s)
{
  while ((s.indexOf(' ',0) == 0) && (s.length > 1))
  {
    s = s.substring(1,s.length);
  }
  while ((s.lastIndexOf(' ') == (s.length - 1) && (s.length > 1)))
  {
    s = s.substring(0,(s.length - 1));
  }
  if ((s.indexOf(' ',0) == 0) && (s.length == 1)) 
    s = '';
  return s;
}

function IsItPresent(s,explanation)
{
  s = StripSpacesFromEnds(s);
  if (s.length)
    return s;
  alert('Please enter ' + explanation + '.');
  return '';
}

function CheckEmail(s_email)
{
  s_email = IsItPresent(s_email,'your email address');
  if (! s_email) 
    return false;
  var i = s_email.indexOf(' ',0);
  while (i > -1)
  {
    s_email = s_email.substring(0,i) + s_email.substring((i + 1),s_email.length);
    i = s_email.indexOf(' ',0);
  }
  document.info.email.value = s_email;
  if ((s_email.length < 6) ||
      (s_email.indexOf('@',0) < 1) ||
      (s_email.lastIndexOf('@') != s_email.indexOf('@',0)) ||
      (s_email.lastIndexOf('@') > (s_email.length - 5)) ||
      (s_email.lastIndexOf('.') > (s_email.length - 3)) ||
      (s_email.lastIndexOf('.') < (s_email.length - 4)) ||
      (s_email.indexOf('..',0) > -1) ||
      (s_email.indexOf('@.',0) > -1) ||
      (s_email.indexOf('.@',0) > -1) ||
      (s_email.indexOf(',',0) > -1))
  {
    alert('The email address "' + s_email + '" is not valid.');
    return false;
  }
  return true;
}