<ssp:EntityForm>
            <ssp:EntityItem Header="Aaaaaa:">
                <TextBox/>
            </ssp:EntityItem>
            <ssp:EntityItem Header="Bbbb:">
                <TextBox/>
            </ssp:EntityItem>
        </ssp:EntityForm>

    public class EntityForm : ItemsControl
    {
        static EntityForm()
        {
            DefaultStyleKeyProperty.OverrideMetadata(
                typeof(EntityForm), 
                new FrameworkPropertyMetadata(typeof(EntityForm))
            );

            IsTabStopProperty.OverrideMetadata(
                typeof(EntityForm),
                new FrameworkPropertyMetadata(false)
            );
        }
    }

    public class EntityItem : HeaderedContentControl
    {
        static EntityItem()
        {
            DefaultStyleKeyProperty.OverrideMetadata(
                typeof(EntityItem),
                new FrameworkPropertyMetadata(typeof(EntityItem))
            );

            IsTabStopProperty.OverrideMetadata(
                typeof(EntityItem),
                new FrameworkPropertyMetadata(false)
            );
        }
    }

    <Style TargetType="{x:Type ssp:EntityForm}">
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type ssp:EntityForm}">
                    <Border Background="{TemplateBinding Background}"
                            BorderBrush="{TemplateBinding BorderBrush}"
                            BorderThickness="{TemplateBinding BorderThickness}"
                            Padding="{TemplateBinding Padding}">

                        <ItemsPresenter/>

                    </Border>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
        <Setter Property="ItemsPanel">
            <Setter.Value>
                <ItemsPanelTemplate>
                    <StackPanel Grid.IsSharedSizeScope="True"/>
                </ItemsPanelTemplate>
            </Setter.Value>
        </Setter>
    </Style>

    <Style TargetType="{x:Type ssp:EntityItem}">
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type ssp:EntityItem}">
                    <Border Background="{TemplateBinding Background}"
                            BorderBrush="{TemplateBinding BorderBrush}"
                            BorderThickness="{TemplateBinding BorderThickness}"
                            Padding="{TemplateBinding Padding}">

                        <Grid>
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition Width="Auto" SharedSizeGroup="HeaderColumn"/>
                                <ColumnDefinition/>
                            </Grid.ColumnDefinitions>

                            <ContentPresenter Grid.Column="0" 
                                              ContentSource="Header"
                                              VerticalAlignment="Center"/>
                            <ContentPresenter Grid.Column="1" 
                                              ContentSource="Content"
                                              VerticalAlignment="Center"/>
                        </Grid>

                    </Border>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>