MarkdownEditControl.xaml

<UserControl
    x:Class="RichMarkdownBox.MarkdownEditControl"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:RichMarkdownBox"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    d:DesignHeight="300"
    d:DesignWidth="400">

    <StackPanel>
        <CommandBar x:Name="commandBar" VerticalContentAlignment="Center" OverflowButtonVisibility="Collapsed" >
            <AppBarToggleButton Icon="Bold" x:Name="BoldButton" Click="TextFormatButton_Click"/>
            <AppBarToggleButton Icon="Italic" x:Name="ItalicButton" Click="TextFormatButton_Click"/>
            <AppBarToggleButton Icon="Underline" x:Name="underLineButton" Click="TextFormatButton_Click"/>
            <CommandBar.Content>
                <ComboBox VerticalAlignment="Center" x:Name="headerSelector" SelectionChanged="ComboBox_SelectionChanged" Tapped="headerSelector_Tapped" DropDownOpened="headerSelector_DropDownOpened" Margin="0,0,0,8">
                    <ComboBoxItem Name="noHeader" Content="No Header"/>
                    <ComboBoxItem Name="h1Button">
                        <TextBlock Text="Heading 1" FontSize="20.5" FontWeight="Bold"/>
                    </ComboBoxItem>
                    <ComboBoxItem Name="h2Button">
                        <TextBlock Text="Heading 2" FontSize="20.5" FontWeight="Medium"/>
                    </ComboBoxItem>
                    <ComboBoxItem Name="h3Button">
                        <TextBlock Text="Heading 3" FontSize="18.3" FontWeight="Bold"/>
                    </ComboBoxItem>
                    <ComboBoxItem Name="h4Button">
                        <TextBlock Text="Heading 4" FontSize="18.3" FontWeight="Medium"/>
                    </ComboBoxItem>
                </ComboBox>
            </CommandBar.Content>
        </CommandBar>
        <local:RichMarkdownBox x:Name="editor" SelectionChanged="editor_SelectionChanged" FontSize="16"/>
    </StackPanel>
</UserControl>