The code below still displays nothing inside the tab. The listbox was added just to ensure that something was visible I could see. It's not the real contents I want.
XML
<Window
x:Class="BattleAnimator.MainWnd"
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:BattleAnimator"
mc:Ignorable="d"
Title="Naval Battle Animator"
Height="450"
Width="800"
WindowStyle="ToolWindow"
ResizeMode="CanResizeWithGrip"
WindowStartupLocation="CenterScreen"
WindowState="Maximized"
FontFamily="Times New Roman">
<Window.Resources>
<DataTemplate
x:Key="TabCtnts">
<ListBox>
<ListBoxItem>t</ListBoxItem>
</ListBox>
</DataTemplate>
<DataTemplate
x:Key="TabHdr">
<StackPanel
Orientation="Horizontal"
DataContext="{Binding DataContext, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type TabItem}}}">
<Label
VerticalAlignment="Center"
VerticalContentAlignment="Center"
MaxWidth="397">
<Label.Content>
<TextBlock
TextTrimming="WordEllipsis"
Text="{Binding Title}"
ToolTip="{Binding Title}" />
</Label.Content>
</Label>
<Button
Click="OnChildNeedsClosed"
ToolTip="Close this script"
Style="{DynamicResource TabBarCloseBtn}"
Background="{x:Null}">✘</Button>
</StackPanel>
</DataTemplate >
<DataTemplate
x:Key="Tab">
<TabItem
ContentTemplate="{DynamicResource TabCtnts}"
HeaderTemplate="{DynamicResource TabHdr}" />
</DataTemplate>
</Window.Resources>
<DockPanel>
<Border
DockPanel.Dock="Top"
BorderBrush="{DynamicResource {x:Static SystemColors.WindowTextBrushKey}}"
BorderThickness="0,0,0,1"
Margin="0,0,0,3"
Padding="0,3,0,0">
<StackPanel
x:Name="toolBar"
Orientation="Horizontal">
<Button
x:Name="btnOpen"
Content="Open"
Click="OnOpenClicked"
Style="{DynamicResource ToolbarBtn}" />
<Separator
Style="{DynamicResource ToolBarSep}" />
<Button
x:Name="btnFullScreen"
Content="Full Screen"
Style="{DynamicResource ToolbarBtn}" />
</StackPanel>
</Border>
<TabControl
x:Name="sheetMain"
ItemTemplate="{DynamicResource TabHdr}"
ContentTemplate="{DynamicResource TabCtnts}" />
</DockPanel>
</Window>