Equation Calculator with Graphing

<UserControl x:Class="Calculator.CalculatorCtrl"
            xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
            xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
            xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
            xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
            xmlns:shared="clr-namespace:CommonUtils;assembly=CommonUtils"
            xmlns:local="clr-namespace:Calculator"
            mc:Ignorable="d" 
            d:DesignHeight="325" d:DesignWidth="471">
    <UserControl.Resources>

        <Style TargetType="ListBoxItem">
            <Style.Resources>
                <!-- 
http://blogs.msdn.com/b/wpfsdk/archive/2007/08/31/specifying-the-selection-color-content-alignment-and-background-color-for-items-in-a-listbox.aspx
-->
                <!--SolidColorBrush x:Key="{x:Static SystemColors.HighlightBrushKey}" Color="LightGreen"/-->
                <SolidColorBrush x:Key="{x:Static SystemColors.ControlBrushKey}" Color="#fF242424"/>
                <SolidColorBrush x:Key="{x:Static SystemColors.HighlightBrushKey}" Color="#FF545454"/>
            </Style.Resources>
            <Setter Property="Foreground" Value="{StaticResource Forecolor}" />
        </Style>

        <DataTemplate DataType="{x:Type shared:EquationParser}">
            <shared:DockWrapPanel Margin="0,-2,0,-2">
                <Label Content="{Binding Equation}" VerticalContentAlignment="Center" Margin="0,0,10,0"/>
                <Label Content="{Binding UsedVarsAsString}" 
                    VerticalContentAlignment="Bottom" FontSize="10" />
                <StackPanel DockPanel.Dock="Right" Orientation="Horizontal" FlowDirection="RightToLeft">
                    <Label Content="{Binding ValueAsString}" MinWidth="20" VerticalContentAlignment="Center" FlowDirection="LeftToRight"/>
                    <Label Content="=" VerticalContentAlignment="Center"/>
                </StackPanel>
            </shared:DockWrapPanel>
        </DataTemplate>

        <SolidColorBrush x:Key="infocolor" Color="Wheat" />
        <shared:VisibilityConverter x:Key="visConv" />

    </UserControl.Resources>
    <Grid >
        <Grid.RowDefinitions>
            <RowDefinition Height="214*" />
            <RowDefinition Height="101" />
        </Grid.RowDefinitions>
        <ListBox ItemsSource="{Binding Stack}" HorizontalContentAlignment="Stretch" 
            ScrollViewer.HorizontalScrollBarVisibility="Disabled" 
            x:Name="m_stackView" Background="Black" TabIndex="4" PreviewKeyDown="OnListboxPreviewKeyDown" />
        <StackPanel Grid.Row="1" Margin="10,0,10,0">
            <StackPanel Orientation="Horizontal">
                <TextBlock Text="Expression" FontFamily="Calibri" FontSize="14" 
                    Foreground="{StaticResource infocolor}" VerticalAlignment="Center"/>
                <TextBlock Margin="8,0,0,0" FontFamily="Calibri" FontSize="12" 
                    Foreground="{StaticResource infocolor}" VerticalAlignment="Center"
                    Visibility="{Binding ElementName=m_input, Path=IsFocused, Converter={StaticResource visConv}}">
                    Enter expression, &lt;Enter&gt; to calculate
                </TextBlock>
            </StackPanel>
            <DockPanel>
                <Button Margin="3,0,0,0" Width="50" VerticalAlignment="Stretch" Click="OnInsertFunction"
                    Style="{StaticResource StyleBlackButton}" TabIndex="2" DockPanel.Dock="Right" x:Name="m_funcButton">Func</Button>
                <Button Margin="3,0,0,0" Width="50" VerticalAlignment="Stretch" Click="OnCalculate"
                    Style="{StaticResource StyleBlackButton}" TabIndex="1" DockPanel.Dock="Right">Calc</Button>
                <shared:TextBoxWithHistory Text=""
                    Name="m_input" 
                    VerticalAlignment="Top"
                    HorizontalAlignment="Stretch"
                    FontSize="16"
                    KeyDown="OnInputKeyDown"
                    SelectionBrush="LightGray"
                    CaretBrush="{Binding RelativeSource={RelativeSource Self}, Path=Foreground}" TabIndex="0">
                </shared:TextBoxWithHistory>
            </DockPanel>
            <StackPanel Orientation="Horizontal" Margin="0,8,0,0">
                <TextBlock Text="Constants" FontFamily="Calibri" FontSize="14" 
                    Foreground="{StaticResource infocolor}" VerticalAlignment="Center"/>
                <TextBlock Margin="8,0,0,0" FontFamily="Calibri" FontSize="12" 
                    Foreground="{StaticResource infocolor}" VerticalAlignment="Center"
                    Visibility="{Binding ElementName=m_variables, Path=IsFocused, Converter={StaticResource visConv}}">
                    Semicolon seperated list e.g. 'x=10; y=pi/2'
                </TextBlock>
            </StackPanel>
            <Border>
                <Border.Resources>
                    <Style x:Key="DropButtonStyle" TargetType="Button" BasedOn="{StaticResource StyleBrownButton}">
                    </Style>
                </Border.Resources>
                <shared:TextBoxWithHistory Text="" HorizontalAlignment="Stretch" 
                        Name="m_variables" 
                        VerticalAlignment="Top"
                        FontSize="12"
                        SelectionBrush="LightGray"
                        CaretBrush="{Binding RelativeSource={RelativeSource Self}, Path=Foreground}" 
                        TabIndex="3">
                    <shared:TextBoxWithHistory.Resources>
                    </shared:TextBoxWithHistory.Resources>
                </shared:TextBoxWithHistory>
            </Border>
        </StackPanel>
    </Grid>
</UserControl>