--- a/Jint.Runtime/VM/Frame.cs	Sun Oct 27 17:23:25 2013 +0400
+++ b/Jint.Runtime/VM/Frame.cs	Sun Oct 27 21:20:59 2013 +0400
@@ -5,7 +5,7 @@
 
 namespace Jint.Runtime.VM {
     class Frame {
-        IBox[] m_registers;
+        AbstractBox[] m_registers;
         RuntimeContext m_runtime;
 
         public Frame(int size, RuntimeContext runtime) {
@@ -14,10 +14,10 @@
             if (size < 0)
                 throw new ArgumentOutOfRangeException("size");
             m_runtime = runtime;
-            m_registers = new IBox[size];
+            m_registers = new AbstractBox[size];
         }
 
-        public IBox this[int index] {
+        public AbstractBox this[int index] {
             get {
                 return m_registers[index];
             }
@@ -26,14 +26,31 @@
             }
         }
 
+        /// <summary>
+        /// Extracts value stored in the registry specified by the index.
+        /// </summary>
+        /// <remarks>This method doesn't do any cast, if the specified type isn't the same as the type of the stored value a type cast exception will occur.</remarks>
+        /// <typeparam name="T">The type of the value stored in the registry.</typeparam>
+        /// <param name="index">The index of the registry.</param>
+        /// <returns>The value stored in the registry.</returns>
         public T GetValue<T>(int index) {
-            // TODO handle conversion errors
             return ((Box<T>)m_registers[index]).holdingValue;
         }
 
+        /// <summary>
+        /// Stores a new value in the register specified by the index.
+        /// </summary>
+        /// <remarks>
+        /// If the previous value has the same type as the value being stored in the registry,
+        /// the new value will replace the old one, otherwise the registry will be reallocated to
+        /// store the new value.
+        /// </remarks>
+        /// <typeparam name="T">The type of the value being stored</typeparam>
+        /// <param name="index">The index of the registry where the value will be stored</param>
+        /// <param name="value">The value to be stored in the registry</param>
         public void SetValue<T>(int index, T value) {
             var reg = m_registers[index] as Box<T>;
-            if (reg == null)
+            if (reg == null || reg.holdingType != typeof(T))
                 m_registers[index] = m_runtime.BoxValue(value);
             else
                 reg.holdingValue = value;