myaac/system/templates/admin.notepad.html.twig

<div class="row">
    <div class="col-md-6">
        <div class="box box-danger">
            <div class="box-header with-border">
                <h3 class="box-title">Notepad</h3>
            </div>
            <form method="post">
                <div class="box-body">
                    <div class="form-group">
                        <label>This is your personal notepad. Be sure to save it each time you modify something.</label>
                        <textarea class="form-control" style="text-align: left;" name="content" cols="50" rows="15"
                                  onchange="notepad_onchange(this);">{% if content is not null %}{{ content }}{% endif %}</textarea>
                    </div>
                </div>
                <div class="box-footer">
                    <button name="submit" onclick="notepad_save(this);" value="Save" class="btn btn-primary">Save
                    </button>
                </div>
            </form>
        </div>
    </div>
</div>

{# <?php echo isset($_content) ? htmlentities($_content, ENT_COMPAT, 'UTF-8') : ''; ?> #}

{# confirm leaving current page if content of the notepad has been modified #}

<script type="text/javascript">
    var original_value = document.getElementsByName("content")[0].value;

    function confirm_exit(e) {
        var e = e || window.event;
        var message = 'Are you sure you want to quit? Remaining changes will be unsaved.';

        // for IE and Firefox prior to version 4
        if (e) {
            e.returnValue = message;
        }

        // for Safari
        return message;
    }

    function notepad_onchange(e) {
        if (original_value != e.value) {
            window.onbeforeunload = confirm_exit;
        }
        return true;
    }

    function notepad_save(e) {
        window.onbeforeunload = function (e) {
        };
        return true;
    }
</script>