我以前只和阿瓦隆合作过一次，所以我做了一个快速的项目，做你想要的。
作为一个免责声明，AvalonEdit似乎破坏了任何尝试，把一个边界周围，如你所说。所以我设置它使用网格，把一个边界周围。
它看起来像这样：

代码如下所示：

<Window x:Class="WpfApplication1.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Width="600" Height="500"
    xmlns:avalonEdit="http://icsharpcode.net/sharpdevelop/avalonedit">
<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="Auto" />
        <RowDefinition Height="Auto" />
        <RowDefinition Height="*" />
        <RowDefinition Height="Auto" />
    </Grid.RowDefinitions>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="Auto" />
        <ColumnDefinition />
    </Grid.ColumnDefinitions>

    <Label Grid.Column="0" Grid.Row="0" Content="Account:" HorizontalAlignment="Left" Margin="20,20" VerticalAlignment="Top" Height="26" Width="56" />
    <TextBox Grid.Column="1" Grid.Row="0" Name="textBoxAccount" HorizontalAlignment="Left" Height="26" Margin="20" TextWrapping="Wrap"
             VerticalAlignment="Top" Width="120" />
    <Label Grid.Column="0" Grid.Row="1" Content="Query:" HorizontalAlignment="Left" Margin="20,0" VerticalAlignment="Top" Height="26" Width="45" />

    <Border Grid.ColumnSpan="2"
            Grid.Row="2"
            Grid.Column="0" BorderBrush="Black" BorderThickness="1"
            Margin="20"
            Height="230">
        <avalonEdit:TextEditor
            x:Name="textEditor"
            FontFamily="Consolas"
            SyntaxHighlighting="AWQL"
            ScrollViewer.VerticalScrollBarVisibility="Hidden"
            WordWrap="True"
            Visibility="Visible"
            FontSize="10pt" VerticalAlignment="Top" Height="226"/>
    </Border>

    <Button Grid.Column="0" Grid.Row="3" x:Name="btnGo" Content="Go!" HorizontalAlignment="Left" Height="25" Margin="20"
            VerticalAlignment="Top" Width="146" />

</Grid>

• • 这并不是您想要的，但从长远来看，网格将有助于解决其他问题**

这是avalonEdit：文本编辑器样式（TextEditor.xaml）：

<Style TargetType="{x:Type AvalonEdit:TextEditor}">
    <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.WindowTextBrushKey}}" />
    <Setter Property="Background" Value="{DynamicResource {x:Static SystemColors.WindowBrushKey}}" />
    <Setter Property="FlowDirection" Value="LeftToRight"/> <!-- AvalonEdit does not support RTL, so ensure we use LTR by default -->
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type AvalonEdit:TextEditor}">
                <ScrollViewer
                    Focusable="False"
                    Name="PART_ScrollViewer"
                    CanContentScroll="True"
                    VerticalScrollBarVisibility="{TemplateBinding VerticalScrollBarVisibility}"
                    HorizontalScrollBarVisibility="{TemplateBinding HorizontalScrollBarVisibility}"
                    Content="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=TextArea}"
                    VerticalContentAlignment="Top"
                    HorizontalContentAlignment="Left"
                    Background="{TemplateBinding Background}"
                    Padding="{TemplateBinding Padding}"
                    BorderBrush="{TemplateBinding BorderBrush}"
                    BorderThickness="{TemplateBinding BorderThickness}"
                />
                <ControlTemplate.Triggers>
                    <Trigger Property="WordWrap"
                             Value="True">
                        <Setter TargetName="PART_ScrollViewer"
                                Property="HorizontalScrollBarVisibility"
                                Value="Disabled" />
                    </Trigger>
                </ControlTemplate.Triggers>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

下面是关于为什么ScrollViewer不显示边框的解释：https://social.msdn.microsoft.com/Forums/vstudio/en-US/a2310302-167b-44e2-bc23-825ff1610701/scrollviewer-border
所以，我认为最好的方法是像Guerudo所说的那样将TextEditor Package 在一个边框内，或者用Avalon代码TextEditor.xaml修改模板。

我没有使用avalonEdit，但我可以给你另一个建议：您可以将TextEditor Package 在<Border> </Border>中。
这可能不是最好的解决方案，但它是一个。

AvalonEdit社区通过更改项目中的TextEditor样式很好地解决了此问题：

<Setter Property="Template">
    <Setter.Value>
        <ControlTemplate TargetType="{x:Type AvalonEdit:TextEditor}">
            <Border
                Background="{TemplateBinding Background}"
                BorderBrush="{TemplateBinding BorderBrush}"
                BorderThickness="{TemplateBinding BorderThickness}">
                <ScrollViewer
                    Focusable="False"
                    Name="PART_ScrollViewer"
                    CanContentScroll="True"
                    VerticalScrollBarVisibility="{TemplateBinding VerticalScrollBarVisibility}"
                    HorizontalScrollBarVisibility="{TemplateBinding HorizontalScrollBarVisibility}"
                    Content="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=TextArea}"
                    VerticalContentAlignment="Top"
                    HorizontalContentAlignment="Left"
                    Padding="{TemplateBinding Padding}"
                />
            </Border>