Added plain TextBox to test the databinding on CodeTextBox.

Befunge/Befunge.sln.DotSettings

@@ -1,2 +1,3 @@
 <wpf:ResourceDictionary xml:space="preserve" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:s="clr-namespace:System;assembly=mscorlib" xmlns:ss="urn:shemas-jetbrains-com:settings-storage-xaml" xmlns:wpf="http://schemas.microsoft.com/winfx/2006/xaml/presentation">
+	<s:Boolean x:Key="/Default/CodeInspection/CodeAnnotations/NamespacesWithAnnotations/=Befunge_002EEditor_002EAnnotations/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/CodeInspection/CodeAnnotations/NamespacesWithAnnotations/=Befunge_002EInterpreter_002EAnnotations/@EntryIndexedValue">True</s:Boolean></wpf:ResourceDictionary>

Befunge/Editor/Editor.csproj

@@ -66,6 +66,7 @@
     <Compile Include="CharStyles\BefungeStyler.cs" />
     <Compile Include="CharStyles\ITextStyler.cs" />
     <Compile Include="Controls\CodeTextBox.cs" />
+    <Compile Include="Properties\Annotations.cs" />
     <Compile Include="Utils\Extensions.cs" />
     <Compile Include="MainWindow.xaml.cs">
       <DependentUpon>MainWindow.xaml</DependentUpon>

Befunge/Editor/MainWindow.xaml

@@ -1,12 +1,22 @@
-<Window x:Class="Befunge.Editor.MainWindow"
+<Window
         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:loc="clr-namespace:Befunge.Editor.Controls"
+        xmlns:local="clr-namespace:Befunge.Editor" x:Class="Befunge.Editor.MainWindow"
         mc:Ignorable="d"
         Title="Befunge Editor" Height="350" Width="525">
+    <Window.DataContext>
+        <local:TextContext/>
+    </Window.DataContext>
     <Grid>
-        <loc:CodeTextBox x:Name="EditRegion" Margin="10,10,10,10.5" Text="Hello, world!"/>
+        <Grid.RowDefinitions>
+            <RowDefinition Height="1*"/>
+            <RowDefinition Height="1*"/>
+        </Grid.RowDefinitions>
+        
+        <loc:CodeTextBox x:Name="EditRegion" Margin="10" Text="{Binding Text, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Grid.Row="0"/>
+        <TextBox x:Name="PlainTextBox" Margin="10" Text="{Binding Text, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Grid.Row="1"/>
     </Grid>
 </Window>

Befunge/Editor/MainWindow.xaml.cs

@@ -1,8 +1,34 @@
-using System.Windows;
+using System.ComponentModel;
+using System.Runtime.CompilerServices;
+using System.Windows;
+using Befunge.Editor.Annotations;
 using Befunge.Editor.CharStyles;
 
 namespace Befunge.Editor
 {
+    public class TextContext : INotifyPropertyChanged
+    {
+        private string _text;
+
+        public string Text
+        {
+            get { return _text; }
+            set
+            {
+                _text = value;
+                OnPropertyChanged(nameof(Text));
+            }
+        }
+
+        public event PropertyChangedEventHandler PropertyChanged;
+
+        [NotifyPropertyChangedInvocator]
+        protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
+        {
+            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
+        }
+    }
+
     public partial class MainWindow
     {
         public MainWindow()

Befunge/Interpreter/IStepInterpreter.cs

@@ -4,7 +4,7 @@ using System.Threading.Tasks;
 
 namespace Befunge.Interpreter
 {
-    public interface StepInterpreter : INotifyPropertyChanged
+    public interface IStepInterpreter : INotifyPropertyChanged
     {
         IVec2 InstructionPointerPosition { get; }
         string Output { get; }