Some quality of life improvements.

src/NTwain/Data/TWAINH_EXTRAS.cs

@@ -227,6 +227,16 @@ public struct STS
     //  return new STS { RC = rc };
     //}
 
+    /// <summary>
+    /// Quick check if the RC is success.
+    /// </summary>
+    public bool IsSuccess => RC == TWRC.SUCCESS;
+
+    /// <summary>
+    /// Quick access to condition code.
+    /// </summary>
+    public TWCC ConditionCode => STATUS.ConditionCode;
+
     public override string ToString()
     {
       return $"{RC} - {STATUS.ConditionCode}";
@@ -647,10 +657,16 @@ public override string ToString()
   }
   partial struct TW_IDENTITY_LEGACY
   {
+    /// <summary>
+    /// A simplified check on whether this has valid data from DSM.
+    /// </summary>
+    public bool HasValue => Id == 0 && ProtocolMajor == 0 && ProtocolMinor == 0;
+
     public override string ToString()
     {
       return $"{Manufacturer} - {ProductName} v{Version.MajorNum}.{Version.MinorNum} (TWAIN {ProtocolMajor}.{ProtocolMinor})";
     }
+
     public static implicit operator TW_IDENTITY(TW_IDENTITY_LEGACY value) => new()
     {
       Id = value.Id,
@@ -820,6 +836,7 @@ partial struct TW_DEVICEEVENT
     // provide casted versions over raw value
 
     public TWDE Event { get { return (TWDE)_Event; } }
+
     public TWFL FlashUsed2 { get { return (TWFL)_FlashUsed2; } }
   }
 

src/NTwain/TwainAppSession.Caps.cs

@@ -287,6 +287,20 @@ public STS SetCap(ref TW_CAPABILITY value)
       return WrapInSTS(rc);
     }
 
+    /// <summary>
+    /// A simpler cap value setter for common one-value scenarios
+    /// that's easier to use. Not for other container type sets.
+    /// </summary>
+    /// <typeparam name="TValue"></typeparam>
+    /// <param name="cap"></param>
+    /// <param name="value"></param>
+    /// <returns></returns>
+    public STS SetCap<TValue>(CAP cap, TValue value) where TValue : struct
+    {
+      var twcap = ValueWriter.CreateOneValueCap(cap, this, value);
+      return SetCap(ref twcap);
+    }
+
     /// <summary>
     /// Sets a CAP's constraint values.
     /// An easy way to create a value is to use the 

src/NTwain/TwainAppSession.PropEvents.cs

@@ -134,10 +134,15 @@ public byte[]? CustomDsData
     public event TwainEventDelegate<TW_IDENTITY_LEGACY>? DefaultSourceChanged;
 
     /// <summary>
-    /// Fires when <see cref="CurrentSource"/> changes.
+    /// Fires when <see cref="CurrentSource"/> changes (opened and closed).
     /// </summary>
     public event TwainEventDelegate<TW_IDENTITY_LEGACY>? CurrentSourceChanged;
 
+    /// <summary>
+    /// Fires when source has moved from enabled to disabled state.
+    /// </summary>
+    public event TwainEventDelegate<TW_IDENTITY_LEGACY>? SourceDisabled;
+
     /// <summary>
     /// Fires when the source has some device event happening.
     /// </summary>

src/NTwain/TwainAppSession.Sources.cs

@@ -142,6 +142,7 @@ public STS DisableSource()
       if (rc == TWRC.SUCCESS)
       {
         State = STATE.S4;
+        SourceDisabled?.Invoke(this, _currentDS);
       }
       return WrapInSTS(rc);
     }

src/NTwain/TwainAppSession.cs

@@ -228,12 +228,13 @@ public STS CloseDSM()
     }
 
     /// <summary>
-    /// Wraps return code with additional status if not successful.
+    /// Wraps a return code with additional status if not successful.
+    /// Use this right after an API call to get its condition code.
     /// </summary>
     /// <param name="rc"></param>
     /// <param name="dsmOnly">true to get status for dsm operation error, false to get status for ds operation error,</param>
     /// <returns></returns>
-    protected STS WrapInSTS(TWRC rc, bool dsmOnly = false)
+    public STS WrapInSTS(TWRC rc, bool dsmOnly = false)
     {
       if (rc != TWRC.FAILURE) return new STS { RC = rc };
       var sts = new STS { RC = rc, STATUS = GetLastStatus(dsmOnly) };