Wpf: XAML won't render left curly bracket in button content

[JeroenOortwijn]

• .NET Core Version: 3.1.202
• Windows version: 10.0.18363
• Does the bug reproduce also in WPF for .NET Framework 4.8?: Yes

• Is this bug related specifically to tooling in Visual Studio (e.g. XAML Designer, Code editing, etc...)? Yes, filed a bug report, but it was closed and redirected here.

  Problem description:

  XAML designer won’t show left curly bracket if it’s defined with its decimal reference.

  Actual behavior:

Building gives the following build error:

MC3074
The tag '' does not exist in XML namespace https://schemas.microsoft.com/winfx/2006/xaml/presentation'. Line 13 Position 17.

Expected behavior:

Minimal repro:

<Window x:Class="Accolade_xaml_test.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:Accolade_xaml_test"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <WrapPanel>
        <Button Content="&#120;" FontSize="40" Width="40"/>
        <Button Content="&#121;" FontSize="40" Width="40"/>
        <Button Content="&#122;" FontSize="40" Width="40"/>
        <Button Content="&#123;" FontSize="40" Width="40"/> <!-- This should show left curly bracket { -->
        <Button Content="&#124;" FontSize="40" Width="40"/>
        <Button Content="&#125;" FontSize="40" Width="40"/>
        <Button Content="&#126;" FontSize="40" Width="40"/>
    </WrapPanel>
</Window>

[JeroenOortwijn]

On a similar note, it won't show low line when followed by line feed:

        <Button Content="&#95;" FontSize="40" Width="40"/>
        <Button Content="&#95;&#10;" FontSize="40" Width="40"/> <!-- This should show low line _ -->
        <Button Content="&#96;" FontSize="40" Width="40"/>
        <Button Content="&#96;&#10;" FontSize="40" Width="40"/>

[weltkante]

Not rendering left curly bracket is by design and documented in several places, for example here. Reason is that the curly bracket character has special meaning and is used for markup extensions. You have to use {} as escape sequence.

[fabiant3]

Thanks @weltkante for the follow up.