function validEmail(email) {
    if (email=="" || email== null) {
        return false;
    } else {
        var emailReg = /^.+\@(\[?)[a-zA-Z0-9\-\.]+\.([a-zA-Z]{2,6}|[0-9]{1,3})(\]?)$/; // valid
        if (!emailReg.test(email)) { // if syntax is valid
            return false;
        }
        return true;
    }
}

function chkSheet(sheet) {
    if (document.sheet.m_name.value=="") {
        alert(errorNoName);
        document.sheet.m_name.focus();
        return false;
    
    } else if (document.sheet.m_email.value=="") {
        alert(errorNoEmail);
        document.sheet.m_email.focus();
        return false; 
        
    } if (!validEmail(sheet.m_email.value)) {
        alert(errorNoValidEmail);
        sheet.m_email.focus();
        return false;
                
    } else if (document.sheet.m_address.value=="") {
        alert(errorNoAddress);
        document.sheet.m_address.focus();
        return false; 
        
    } else if (document.sheet.m_size.value=="") {
        alert(errorNoSize);
        document.sheet.m_size.focus();
        return false; 
        
    } else if (document.sheet.m_tall.value=="") {
        alert(errorNoTall);
        document.sheet.m_tall.focus();
        return false;                    

    }
    return true;
}