一个控件的多个参数被绑定

前台代码<xaml>
<Window x:Class="WpfApplication4.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Window1" Height="300" Width="300" WindowState="Normal" WindowStartupLocation="CenterScreen">
<Grid Margin="5">
<Grid.RowDefinitions>
<RowDefinition Height="Auto"></RowDefinition>
<RowDefinition Height="Auto"></RowDefinition>
<RowDefinition Height="Auto"></RowDefinition>
<RowDefinition Height="Auto"></RowDefinition>
</Grid.RowDefinitions>
<Slider Name="sliderFontSize" Grid.Row="0" Margin="3" Minimum="1" Maximum="40" Value="10"></Slider>
<TextBox Name="txtContent" Margin="3" Grid.Row="1">Sample Content</TextBox>
<ListBox Margin="3" Grid.Row="2" Name="lstColors">
<ListBoxItem Tag="Blue">Blue</ListBoxItem>
<ListBoxItem Tag="DarkBlue">DarkBlue</ListBoxItem>
<ListBoxItem Tag="Light Blue">Light Blue</ListBoxItem>
</ListBox>
<TextBlock Grid.Row="3" Name="lbSampleText"
FontSize="{Binding ElementName=sliderFontSize,Path=Value}"
Text="{Binding ElementName=txtContent,Path=Text}"
Foreground="{Binding ElementName=lstColors,Path=SelectedItem.Tag}"></TextBlock>
</Grid>
</Window>