function checkForm()
{
   var cname, cemail, csubject, cmessage, caddress;
   with(window.document.msgform)
   {
      cname    = name;
      cemail   = email;
      ctelephone = telephone;
      csubject = subject;
      cmessage = comments;
	  caddress = sender_address;
   }
   
   if(trim(cname.value) == '') {
      alert('Please enter your name.');
      cname.focus();
      return false;
   }
   else if(trim(cname.value).length > 30) {
      alert('Name must not be over 30 characters long.');
      cname.focus();
      return false;
   }
   else if(trim(cemail.value) == '') {
      alert('Please enter your email.');
      cemail.focus();
      return false;
   }
   else if(trim(cemail.value).length > 50) {
      alert('Email must not be over 50 characters long.');
      cemail.focus();
      return false;
   }
   else if(!isEmail(trim(cemail.value))) {
      alert('Email address is not valid.');
      cemail.focus();
      return false;
   }
   else if(trim(ctelephone.value).length > 30) {
      alert('Telephone number must not be over 30 characters long.');
      ctelephone.focus();
      return false;
   }
   else if(trim(ctelephone.value) != "" && !isValidTelephoneNum(trim(ctelephone.value))) {
      alert('Telephone number is not valid.');
      ctelephone.focus();
      return false;
   }
   else if(trim(caddress.value) == '') {
		alert('Please enter your address.');
		caddress.focus();
		return false;
   }
   else if(trim(caddress.value).length > 200) {
	alert('Address must not be over 200 characters long.');
	caddress.focus();
	return false;
   }
   else if(trim(csubject.value) == '') {
      alert('Please enter your message subject.');
      csubject.focus();
      return false;
   }
   else if(trim(cmessage.value) == '') {
      alert('Please enter your message.');
      cmessage.focus();
      return false;
   }
   else {
      cname.value        = trim(cname.value);
      cemail.value       = trim(cemail.value);
      ctelephone.value   = trim(ctelephone.value);
      csubject.value     = trim(csubject.value);
      cmessage.value     = trim(cmessage.value);
      return true;
   }
}

function trim(str)
{
   // g after the closing / indicating end of string means "global", mainly used for search and replace operation
   return str.replace(/^\s+|\s+$/g,'');
}

function isValidTelephoneNum(str)
{
   // / is the start or end of the regular expression
   // ^ is the beginning of a string
   // $ is the end of a string
   // ? is 0 or 1, * is 0 or more, + is 1 or more
   // [] things within square brackets are alternatives - whichever one matches first
   // \ is the escape character for such things as + *, in order to treat them as literals
   // \d means digit, \s means space character
   var regex = /^\+?[\-\s()0-9]+$/;
   
   if(str.match(regex)) {
      return true;
   }
   else {
      return false;
   }
   //   return regex.test(str);
}

function isEmail(str)
{
   // /i at the end means that it is a case-insensitive search
   var regex = /^[-_.a-z0-9]+@(([-_a-z0-9]+\.)+(ad|ae|aero|af|ag|ai|al|am|an|ao|aq|ar|arpa|as|at|au|aw|az|ba|bb|bd|be|bf|bg|bh|bi|biz|bj|bm|bn|bo|br|bs|bt|bv|bw|by|bz|ca|cc|cd|cf|cg|ch|ci|ck|cl|cm|cn|co|com|coop|cr|cs|cu|cv|cx|cy|cz|de|dj|dk|dm|do|dz|ec|edu|ee|eg|eh|er|es|et|eu|fi|fj|fk|fm|fo|fr|ga|gb|gd|ge|gf|gh|gi|gl|gm|gn|gov|gp|gq|gr|gs|gt|gu|gw|gy|hk|hm|hn|hr|ht|hu|id|ie|il|in|info|int|io|iq|ir|is|it|jm|jo|jp|ke|kg|kh|ki|km|kn|kp|kr|kw|ky|kz|la|lb|lc|li|lk|lr|ls|lt|lu|lv|ly|ma|mc|md|mg|mh|mil|mk|ml|mm|mn|mo|mp|mq|mr|ms|mt|mu|museum|mv|mw|mx|my|mz|na|name|nc|ne|net|nf|ng|ni|nl|no|np|nr|nt|nu|nz|om|org|pa|pe|pf|pg|ph|pk|pl|pm|pn|pr|pro|ps|pt|pw|py|qa|re|ro|ru|rw|sa|sb|sc|sd|se|sg|sh|si|sj|sk|sl|sm|sn|so|sr|st|su|sv|sy|sz|tc|td|tf|tg|th|tj|tk|tm|tn|to|tp|tr|tt|tv|tw|tz|ua|ug|uk|um|us|uy|uz|va|vc|ve|vg|vi|vn|vu|wf|ws|ye|yt|yu|za|zm|zw)|(([0-9][0-9]?|[0-1][0-9][0-9]|[2][0-4][0-9]|[2][5][0-5])\.){3}([0-9][0-9]?|[0-1][0-9][0-9]|[2][0-4][0-9]|[2][5][0-5]))$/i;

   if(str.match(regex)) {
      return true;
   }
   else {
      return false;
   }
   //   return regex.test(str);
}