Page.xaml.xml

<!-- replace Page.xaml with this markup -->
<UserControl x:Class="CalculatorTestApp.Page"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:calculator="clr-namespace:CalculatorProject;assembly=Calculator"
    Width="440" Height="320">
    <Border BorderBrush="Gray" BorderThickness="5" CornerRadius="8" Background="LightGray" Padding="3">
        <Grid x:Name="LayoutRoot">
            <Grid.ColumnDefinitions>
                <ColumnDefinition />
                <ColumnDefinition />
            </Grid.ColumnDefinitions>
            <Grid.RowDefinitions>
                <RowDefinition Height="Auto"/>
                <RowDefinition Height="*"/>
                <RowDefinition Height="Auto"/>
            </Grid.RowDefinitions>
            <calculator:Calculator
                Grid.Column="0"
                Grid.Row="0"
                Grid.RowSpan="3"
                Width="200"
                Height="300"
                x:Name="Calculator"/>
            <StackPanel
                Margin="2"
                Grid.Column="1"
                Grid.Row="0"
                Orientation="Horizontal"
                x:Name="FunctionDefinitions">
            </StackPanel>
            <TextBox
                Grid.Column="1"
                Grid.Row="1"
                Margin="2"
                VerticalScrollBarVisibility="Auto"
                HorizontalScrollBarVisibility="Auto"
                MaxHeight="1000"
                AcceptsReturn="True"
                x:Name="Functions" />
            <StackPanel
                Grid.Column="1"
                Grid.Row="2"
                Orientation="Horizontal"
                HorizontalAlignment="Right"
                >
                <Button x:Name="LoadFunctions" Content="Load" Margin="2" />
                <Button x:Name="SaveFunctions" Content="Save" Margin="2" />
            </StackPanel>
        </Grid>
    </Border>
</UserControl>