/**
	 * Check some designated fields of the given form object.
	 * 
	 * @author R.J.T. de Vries <rdevries@thirdwave.nl>
	 * @param 	object	f		form to check
	 * @return 	boolean			true if all fields are filled in correct, false if not.
	 */
	function checkFields(f) {
	
		if ( f.contactname.value == '' ) {
	
			alert ("Vul in ieder geval uw naam in.");
			
			f.contactname.focus();
	
			return false;
	
		}
	
		if ( f.email.value == '' && f.phone.value == '' ) {
	
			alert ("Vul in ieder geval uw e-mail adres of uw telefoonnummer in.");
	
			f.email.focus();

			return false;
	
		}
	
		return true;
	
	} // checkFields()