function checkEnter(e){ //e is event object passed from function invocation
    //var characterCode literal character code will be stored in this variable

    if(e && e.which){ //if which property of event object is supported (NN4)
        e = e;
        characterCode = e.which; //character code is contained in NN4's which property
    }
    else{
        e = event;
        characterCode = e.keyCode; //character code is contained in IE's keyCode property
    }

    if(characterCode == 13){ //if generated character code is equal to ascii 13 (if enter key)
        UserAction('Login'); //submit the form
        return false
    }
    else{
        return true
    }

}