Add comments about expected result after a ConvertTo() call.

This method has grown a few cases where it doesn't actually convert.

ICSharpCode.Decompiler/CSharp/TranslatedExpression.cs

@@ -163,7 +163,7 @@ namespace ICSharpCode.Decompiler.CSharp
 			}
 			throw new ArgumentException("descendant must be a descendant of the current node");
 		}
-		
+
 		/// <summary>
 		/// Adds casts (if necessary) to convert this expression to the specified target type.
 		/// </summary>
@@ -176,6 +176,17 @@ namespace ICSharpCode.Decompiler.CSharp
 		/// 
 		/// From the caller's perspective, IntPtr/UIntPtr behave like normal C# integers except that they have native int size.
 		/// All the special cases necessary to make IntPtr/UIntPtr behave sanely are handled internally in ConvertTo().
+		/// 
+		/// Post-condition:
+		///    The "expected evaluation result" is the value computed by <c>this.Expression</c>,
+		///    converted to targetType via an IL conv instruction.
+		/// 
+		///    ConvertTo(targetType, allowImplicitConversion=false).Type must be equal to targetType (modulo identity conversions).
+		///      The value computed by the converted expression must match the "expected evaluation result".
+		/// 
+		///    ConvertTo(targetType, allowImplicitConversion=true) must produce an expression that,
+		///      when evaluated in a context where it will be implicitly converted to targetType,
+		///      evaluates to the "expected evaluation result".
 		/// </remarks>
 		public TranslatedExpression ConvertTo(IType targetType, ExpressionBuilder expressionBuilder, bool checkForOverflow = false, bool allowImplicitConversion = false)
 		{