function checkEmail (strng) {
    var error="";
    if (strng == "") {
       error = "Вы не ввели e-mail.\n";
    }

    var emailFilter=/^.+@.+\..{2,3}$/;
    if (!(emailFilter.test(strng))) { 
       error = "Пожалуйста, введите корректный e-mail.\n";
    }
    else {
       var illegalChars = /[\(\)\<\>\,\;\:\\\"\[\]]/
         if (strng.match(illegalChars)) {
          error = "E-mail содержит недопустимые символы.\n";
       }
    }
    return error;    
}


// phone number - strip out delimiters and check for 10 digits

function checkPhone (strng) {
var error = "";
if (strng == "") {
   error = "You didn't enter a phone number.\n";
}

var stripped = strng.replace(/[\(\)\.\-\ ]/g, ''); //strip out acceptable non-numeric characters
    if (isNaN(parseInt(stripped))) {
       error = "The phone number contains illegal characters.";
  
    }
    if (!(stripped.length == 10)) {
	error = "The phone number is the wrong length. Make sure you included an area code.\n";
    } 
return error;
}


// password - between 6-8 chars, uppercase, lowercase, and numeral

function checkPassword (strng) {
var error = "";
if (strng == "") {
   error = "You didn't enter a password.\n";
}

    var illegalChars = /[\W_]/; // allow only letters and numbers
    
    if ((strng.length < 6) || (strng.length > 8)) {
       error = "The password is the wrong length.\n";
    }
    else if (illegalChars.test(strng)) {
      error = "The password contains illegal characters.\n";
    } 
    else if (!((strng.search(/(a-z)+/)) && (strng.search(/(A-Z)+/)) && (strng.search(/(0-9)+/)))) {
       error = "The password must contain at least one uppercase letter, one lowercase letter, and one numeral.\n";
    }  
return error;    
}    


// username - 4-10 chars, uc, lc, and underscore only.

function checkUsername (strng) {
var error = "";
if (strng == "") {
   error = "You didn't enter a username.\n";
}


    var illegalChars = /\W/; // allow letters, numbers, and underscores
    if ((strng.length < 4) || (strng.length > 10)) {
       error = "The username is the wrong length.\n";
    }
    else if (illegalChars.test(strng)) {
    error = "The username contains illegal characters.\n";
    } 
return error;
}       


// non-empty textbox

function isEmpty(strng) {
var error = "";
  if (strng.length == 0) {
     error = "Не все необходимые поля заполнены.\n"
  }
return error;	  
}

// was textbox altered

function isDifferent(strng) {
var error = ""; 
  if (strng != "Can\'t touch this!") {
     error = "You altered the inviolate text area.\n";
  }
return error;
}

// exactly one radio button is chosen

function checkRadio(checkvalue) {
var error = "";
   if (!(checkvalue)) {
       error = "Please check a radio button.\n";
    }
return error;
}

// valid selector from dropdown list

function checkDropdown(choice) {
var error = "";
    if (choice == 0) {
    error = "You didn't choose an option from the drop-down list.\n";
    }    
return error;
}

function validate(formId) {
    var error = false;
    if (formId == 'comment') {
        var mandatory_fields = ['user_name', 'text', 'captcha_input'];    
    } else if (document.getElementById('is_rss').checked) {
        var mandatory_fields = ['captcha_input'];
    } else {
        var mandatory_fields = ['title', 'annotation', 'text', 'captcha_input'];
        if (!error && (error = checkEmail(document.getElementById('email').value))) {
            alert(error);
            return false;
        }    
    }
    for (var i in mandatory_fields) {
        if (error = isEmpty(document.getElementById(mandatory_fields[i]).value)) {
            alert(error);
            break;
        }
    }    
    if (error) {
        return false;
    } else {
        document.getElementById(formId).submit();
    }    
} // validate()