<script type="text/javascript">

        var editorList = new Object();
        var editorLengthArray = [30, 30];
        var counter = 0;

        function isAlphaNumericKey(keyCode) {
            if ((keyCode > 47 && keyCode < 58) || (keyCode > 64 && keyCode < 91)) {
                return true;
            }
            return false;
        }

        function LimitCharacters(editor) {
            editorList[editor.get_id()] = editorLengthArray[counter];
            counter++;

            editor.attachEventHandler("onkeydown", function(e) {
                e = (e == null) ? window.event : e;
                if (isAlphaNumericKey(e.keyCode)) {
                    var maxTextLength = editorList[editor.get_id()];

                    textLength = editor.get_text().trim().length;
                    if (textLength >= maxTextLength) {
                        alert('You are not able to type more than ' + maxTextLength + ' symbols!');

                        var rtfeditor = $find("<%=EdtDesc.ClientID %>");
                        var oValue = rtfeditor.get_text().trim();
                        rtfEditor.set_text(oValue.substring(0, 30));

                        e.returnValue = false;
                    }
                }
            });

            var element = document.all ? editor.get_document().body : editor.get_document();
            $telerik.addExternalHandler(element, "paste", function(e) {
                e = (e == null) ? window.event : e;

                var maxTextLength = editorList[editor.get_id()];
                textLength = editor.get_text().length;

                var clipboardLength = window.clipboardData.getData("Text").length;
                textLength += clipboardLength;
                if (textLength >= maxTextLength) {
                    alert('You are not able to type more than ' + maxTextLength + ' symbols!');
                    e.returnValue = false;
                    return false;

                }
            });
        }

        function CalculateLength(editor, value) {
            var textLength = editor.get_text().length;
            var clipboardLength = value.length;
            textLength += clipboardLength;
            return textLength;
        }

        function OnClientPasteHtml(editor, args) {
            var maxTextLength = editorList[editor.get_id()];
            var commandName = args.get_commandName();
            var value = args.get_value();

            if (commandName == "PasteFromWord"
                || commandName == "PasteFromWordNoFontsNoSizes"
                || commandName == "PastePlainText"
                || commandName == "PasteAsHtml"
                || commandName == "Paste") {
                var textLength = CalculateLength(editor, value);
                if (textLength >= maxTextLength) {
                    alert('You are not able to type more than ' + maxTextLength + ' symbols!');
                    args.set_cancel(true);

                }
            }
        }       
       
    </script>