// form validation function //
function validate(form) {
  
  var name = form.name.value;
  var email = form.email.value;
  var institution = form.institution.value;
  var address = form.address.value;
  var nameRegex = /^[a-zA-Z]+(([\'\,\.\- ][a-zA-Z ])?[a-zA-Z]*)*$/;
  var emailRegex = /^[\w-\.]+@([\w-]+\.)+[\w-]{2,4}$/;
  var messageRegex = new RegExp(/<\/?\w+((\s+\w+(\s*=\s*(?:".*?"|'.*?'|[^'">\s]+))?)+\s*|\s*)\/?>/gim);
  
  if(name == "") {
    alert('You must enter your name.')
    return false;
  }
  if(!name.match(nameRegex)) {
    alert('You have entered an invalid name.')
    return false;
  }
  if(email == "") {
    alert('you must enter your email address')
    return false;
  }
  if(!email.match(emailRegex)) {
    alert('You have entered an invalid email address.')
    return false;
  }
  if(institution == "") {
    alert('You must enter an institution.')
    return false;
  }
  if(address == "") {
    alert('You must enter an address.')
    return false;
  }
  if(address.match(messageRegex)) {
    alert('You have entered an invalid address.')
    return false;
  }
  return true;
}