OOP in the Real World - Creating an Equation Editor

<Window
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:Editor"
        x:Class="Editor.MainWindow"
        Title="MainWindow" 
        Height="550" Width="720"  
        WindowStartupLocation="CenterScreen" 
        Background="White"
        TextInput="Window_TextInput"
        KeyDown="Window_KeyDown"      
    >
    <Window.Resources>
        <Style TargetType="{x:Type Image}" x:Key="DisabledImageStyle">
            <Style.Triggers>
                <Trigger Property="IsEnabled"  Value="False">
                    <Setter Property="Opacity" Value="0.4"/>
                </Trigger>
            </Style.Triggers>
        </Style>
    </Window.Resources>
    <Window.CommandBindings>
        <CommandBinding Command="Close"	        Executed="CloseCommandHandler"/>
        <CommandBinding Command="DecreaseZoom"  Executed="DecreaseZoomCommandHandler"/>
        <CommandBinding Command="IncreaseZoom"  Executed="IncreaseZoomCommandHandler"/>
    </Window.CommandBindings>

    <DockPanel x:Name="mainDock" LastChildFill="True">
        <Grid DockPanel.Dock="Top">            
            <Menu DockPanel.Dock="Top">
                <MenuItem x:Name="fileMenuItem" Header="_File">
                    <MenuItem x:Name="exportMenuItem" Header="_Export">
                        <MenuItem Header="_PNG" Click="exportMenuItem_Click"  Tag="png" />
                        <MenuItem Header="_JPG" Click="exportMenuItem_Click"  Tag="jpg"/>
                        <MenuItem Header="_GIF" Click="exportMenuItem_Click"  Tag="gif"/>
                        <MenuItem Header="_BMP" Click="exportMenuItem_Click"  Tag="bmp"/>
                        <MenuItem Header="_TIFF" Click="exportMenuItem_Click" Tag="tif"/>
                        <MenuItem Header="_WMP" Click="exportMenuItem_Click"  Tag="wdp"/>
                    </MenuItem>
                    <!--<MenuItem x:Name="printMenuItem" Header="_Print"    Command="Print"/>-->
                    <MenuItem x:Name="exitMenuItem" Header="E_xit"  Command="Close"/>
                </MenuItem>           
                <MenuItem x:Name="helpMenuItem" Header="_Help">                    
                    <MenuItem x:Name="contentsMenuItem" Header="_Contents (Web)" Click="contentsMenuItem_Click"/>
                    <MenuItem x:Name="supportMenuItem" Header="_Support (Web)" Click="supportMenuItem_Click"/>
                    <MenuItem x:Name="aboutMenuItem" Header="_About" Click="aboutMenuItem_Click"/>
                </MenuItem>
            </Menu>
        </Grid>
        <Grid DockPanel.Dock="Top" HorizontalAlignment="Stretch" Margin="0,2,0,4">
            <ToolBarTray  IsLocked="True">
                <ToolBar Band="1" BandIndex="1"  Height="30" Loaded="ToolBar_Loaded">
                    <Button x:Name="zoomoutButton" Command="DecreaseZoom" ToolTip="Zoom out" ToolTipService.ShowOnDisabled="True">
                        <local:AutoGreyableImage Source="images\gui\zoomout.png"/>
                    </Button>
                    <Button x:Name="zoominButton" Command="IncreaseZoom" ToolTip="Zoom in" ToolTipService.ShowOnDisabled="True">
                        <local:AutoGreyableImage Source="images\gui\zoomin.png" />
                    </Button>
                    <Separator />
                    <ToggleButton x:Name="underbarToggle" ToolTip="Show/Hide Underbar" Unchecked="underbarToggleCheckChanged" Checked="underbarToggleCheckChanged">
                        <Image Source="images\gui\underbar.png" />
                    </ToggleButton>                    
                    <Separator />
                    <Label>
                        <Hyperlink Click="meLinkClick">Download Full Version (Free)</Hyperlink>
                    </Label>
                </ToolBar>
            </ToolBarTray>
        </Grid>
        <local:MathToolBar x:Name="mathToolBar" DockPanel.Dock="Top" DockPanel.ZIndex="99"></local:MathToolBar>
        <Grid Background="#FFEEDDCC" DockPanel.Dock="Bottom" Visibility="Collapsed">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="*"></ColumnDefinition>
                <ColumnDefinition Width="Auto"></ColumnDefinition>
            </Grid.ColumnDefinitions>
            <Label Name="statusBarLeftLabel" Height="25"></Label>
            <Label Grid.Column="1" Name="statusBarRightLabel" Height="25" HorizontalAlignment="Right"></Label>
        </Grid>
        <ScrollViewer x:Name="scrollViwer" FocusVisualStyle="{x:Null}" Focusable="True" ScrollChanged="scrollViwer_ScrollChanged" HorizontalScrollBarVisibility="Auto">
            <local:EditorControl Background="Transparent" x:Name="editor" Focusable="True"  FocusVisualStyle="{x:Null}"></local:EditorControl>
        </ScrollViewer>
    </DockPanel>
</Window>