Maple/Maple.App/EditPage.xaml

<Page
    x:Class="Maple_App.EditPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:Maple_App"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:Windows10FallCreatorsUpdate="http://schemas.microsoft.com/winfx/2006/xaml/presentation?IsApiContractPresent(Windows.Foundation.UniversalApiContract, 5)"
    xmlns:Windows10version1809="http://schemas.microsoft.com/winfx/2006/xaml/presentation?IsApiContractPresent(Windows.Foundation.UniversalApiContract, 7)"
    mc:Ignorable="d"
    NavigationCacheMode="Disabled">

    <Page.Resources>
        <ResourceDictionary>
            <Flyout x:Name="ValidConfigFlyout">
                <StackPanel Orientation="Horizontal">
                    <SymbolIcon Symbol="Accept" VerticalAlignment="Center" Margin="0, 0, 8, 0"/>
                    <TextBlock TextWrapping="Wrap">No error</TextBlock>
                </StackPanel>
            </Flyout>
            <Flyout x:Name="InvalidConfigFlyout">
                <StackPanel Orientation="Horizontal">
                    <SymbolIcon Symbol="Important" VerticalAlignment="Center" Margin="0, 0, 8, 0"/>
                    <TextBlock TextWrapping="Wrap">
                        <Run>There is an error(s) in your configuration.</Run>
                        <LineBreak/>
                        <Run>Please check carefully and correct them.</Run>
                    </TextBlock>
                </StackPanel>
            </Flyout>
        </ResourceDictionary>
    </Page.Resources>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
        <CommandBar Grid.Row="0" DefaultLabelPosition="Right">
            <CommandBar.PrimaryCommands>
                <AppBarButton x:Name="SaveButton" IsEnabled="False" Icon="Save" Label="Save" Click="SaveButton_Click">
                    <AppBarButton.Command>
                        <Windows10version1809:StandardUICommand Kind="Save"/>
                    </AppBarButton.Command>
                </AppBarButton>
                <AppBarButton Icon="Help" Label="Help" Click="HelpButton_Click">
                    <Windows10FallCreatorsUpdate:AppBarButton.KeyboardAccelerators>
                        <Windows10FallCreatorsUpdate:KeyboardAccelerator Key="F1"/>
                    </Windows10FallCreatorsUpdate:AppBarButton.KeyboardAccelerators>
                </AppBarButton>
            </CommandBar.PrimaryCommands>
        </CommandBar>
        <RichEditBox
            x:Name="EditBox"
            Grid.Row="1"
            FontFamily="Consolas"
            IsColorFontEnabled="True"
            TextChanging="EditBox_TextChanging"/>
    </Grid>
</Page>