问属性元素不能位于元素内容的中间？

EN

<Fluent:RibbonTabItem Header="CT" Group="{Binding ElementName=toolsGroup}"/>

< Fluent:RibbonWindow x:Class="FluentRibbonPractice.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:Fluent="clr-namespace:Fluent;assembly=Fluent"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Fluent:Ribbon>

            <!--Backstage-->
            <Fluent:Ribbon.Menu>
                <Fluent:Backstage>
                    <Fluent:BackstageTabControl>
                        <Fluent:BackstageTabItem Header="New" />
                        <Fluent:BackstageTabItem Header="Print" />
                        <Fluent:Button Header="Blue" Icon="Images\Blue.png" />
                    </Fluent:BackstageTabControl>
                </Fluent:Backstage>
            </Fluent:Ribbon.Menu>

            <!--Tabs-->
            <Fluent:RibbonTabItem Header="Tab">
                <Fluent:RibbonGroupBox Header="Group">
                    <Fluent:Button Name="buttonGreen" Header="Green"
                                   Icon="Images\Green.png" LargeIcon="Images\GreenLarge.png" />
                    <Fluent:Button Name="buttonGray" Header="Gray"
                                   Icon="Images\Gray.png" LargeIcon="Images\GrayLarge.png" />
                </Fluent:RibbonGroupBox>
            </Fluent:RibbonTabItem>

            <!--QAT Items-->
            <Fluent:Ribbon.QuickAccessItems>
                <Fluent:QuickAccessMenuItem IsChecked="true">
                    <Fluent:Button Header="Pink" Icon="Images\Pink.png" />
                    </Fluent:QuickAccessMenuItem>
                    <!--Binding to a control-->
                <Fluent:QuickAccessMenuItem Target="{Binding ElementName=buttonGreen}" />
            </Fluent:Ribbon.QuickAccessItems>


            <!--Contextual Tab Groups-->
            <Fluent:Ribbon.ContextualGroups>
                <Fluent:RibbonContextualTabGroup Header="Tools" Visibility="Visible"
                                                x:Name="toolsGroup" Background="Green" BorderBrush="Green" />
            </Fluent:Ribbon.ContextualGroups>

            <!-- Contextual Tab -->
            <Fluent:RibbonTabItem Header="CT" Group="{Binding ElementName=toolsGroup}"/>

        </Fluent:Ribbon>
    </Grid>
< /Fluent:RibbonWindow>