function isEmail(str) {
  // are regular expressions supported?
  var supported = 0;
  if (window.RegExp) {
    var tempStr = "a";
    var tempReg = new RegExp(tempStr);
    if (tempReg.test(tempStr)) supported = 1;
  }
  if (!supported) 
    return (str.indexOf(".") > 2) && (str.indexOf("@") > 0);
  var r1 = new RegExp("(@.*@)|(\\.\\.)|(@\\.)|(^\\.)");
  var r2 = new RegExp("^.+\\@(\\[?)[a-zA-Z0-9\\-\\.]+\\.([a-zA-Z]{2,4}|[0-9]{1,3})(\\]?)$");
  return (!r1.test(str) && r2.test(str));
}

function check_submission() {

if (document.enquiry.name.value == "")
 { alert("Please enter your name.");
   document.enquiry.name.focus();
   return false;
  }
if (!isEmail(document.enquiry.email.value) && document.enquiry.phone.value =="")
 { alert("Please enter a valid email address or your phone number.");
   document.enquiry.phone.focus();
   return false;
  } 
if (document.enquiry.security_code.value == "")
 { alert("Please enter the security code.");
   document.enquiry.security_code.focus();
   return false;
  } 
}