Custom border for UserControl

I know too little about design to pull this off.

I am trying to make a UserControl with a special border. The border should look like this:

The header is a label (or textblock if is a must) with the content set at init time.

The border must stop before the header and start again after the header with a margin like described. The border will house a frame or grid which must confrom to the border shape (probably with a mask) The entire background must be transparent or alpha-ed (Color #000000XX) which is important because the header cant just "hide" the rectangle by being on top.

I'd appreciate directions to achieve this. Blend from visual studio 2012 is available.

Thank you

here you go

I made use of HeaderedContentControl which allows you to have a header and a content which you can further use in a template of your preference

<HeaderedContentControl x:Class="CSharpWPF.MyUserControl"
                        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
                        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
                        mc:Ignorable="d"
                        d:DesignHeight="300"
                        d:DesignWidth="300"
                        Header="Header">
    <HeaderedContentControl.Template>
        <ControlTemplate TargetType="HeaderedContentControl">
            <Grid>
                <Border BorderBrush="Black"
                        BorderThickness="4"
                        CornerRadius="10"
                        Padding="4"
                        Margin="10">
                    <ContentPresenter />
                </Border>
                <TextBlock Text="{TemplateBinding Header}"
                           Background="White"
                           HorizontalAlignment="Left"
                           VerticalAlignment="Top"
                           FontSize="13"
                           Margin="25,0,0,0"
                           Padding="10,0"/>
            </Grid>
        </ControlTemplate>
    </HeaderedContentControl.Template>
    <Grid>
        <TextBlock Text="content" />
    </Grid>
</HeaderedContentControl>

result

Update

try this template, I did try to achieve by pure xaml

    <HeaderedContentControl.Template>
        <ControlTemplate TargetType="HeaderedContentControl">
            <DockPanel x:Name="root"
                       LastChildFill="True"
                       Margin="10">
                <DockPanel.Resources>
                    <Style TargetType="Border">
                        <Setter Property="BorderBrush"
                                Value="Black" />
                        <Setter Property="Width"
                                Value="30" />
                        <Setter Property="Height"
                                Value="30" />
                        <Setter Property="CornerRadius"
                                Value="10" />
                    </Style>
                </DockPanel.Resources>
                <Grid DockPanel.Dock="Top"
                      Height="20">

                    <Grid.ColumnDefinitions>
                        <ColumnDefinition Width="20" />
                        <ColumnDefinition Width="auto" />
                        <ColumnDefinition Width="*" />
                        <ColumnDefinition Width="20" />
                    </Grid.ColumnDefinitions>
                    <Border BorderThickness="4,4,0,0" />
                    <Border BorderThickness="0,4,0,0"
                            Grid.Column="2"
                            Width="auto"
                            CornerRadius="0" />
                    <Border BorderThickness="0,4,4,0"
                            Grid.Column="3"
                            HorizontalAlignment="Right" />
                    <TextBlock Text="{TemplateBinding Header}"
                               FontSize="13"
                               Grid.Column="1"
                               Margin="10,-10"
                               VerticalAlignment="Top" />
                </Grid>
                <Grid Height="20"
                      DockPanel.Dock="Bottom">
                    <Border BorderThickness="4,0,4,4"
                            Width="auto"
                            VerticalAlignment="Bottom" />
                </Grid>
                <Border BorderThickness="4,0,0,0"
                        DockPanel.Dock="Left"
                        Height="auto"
                        Width="20"
                        CornerRadius="0" />
                <Border BorderThickness="0,0,4,0"
                        DockPanel.Dock="Right"
                        Width="20"
                        Height="auto"
                        CornerRadius="0" />
                <ContentPresenter Margin="-10" />
            </DockPanel>
        </ControlTemplate>
    </HeaderedContentControl.Template>

other approach might include some code behind if this is not suitable

result