diff --git a/onnxruntime/core/providers/cpu/controlflow/scan.cc b/onnxruntime/core/providers/cpu/controlflow/scan.cc
index 0504fe5a2f..2952d5f92e 100644
--- a/onnxruntime/core/providers/cpu/controlflow/scan.cc
+++ b/onnxruntime/core/providers/cpu/controlflow/scan.cc
@@ -119,8 +119,10 @@ class LoopStateVariable {
 };
 
 /*
-Class that co-ordinates writes to slices of the overall Scan output.
-It will directly update the data returned by OpKernelContextInternal.Output(i).
+Class that co-ordinates writing to slices of the overall Scan output buffer returned by OpKernelContext.Output(i). 
+If the subgraph has a symbolic dimension in an output it will use a temporary MLValue for the first execution
+in order to discover the output shape. Once the shape is known, it will switch to using the overall output buffer 
+to avoid copies.
 */
 class OutputIterator {
  public:
@@ -136,6 +138,7 @@ class OutputIterator {
   MLValue& operator*();
   OutputIterator& operator++();
 
+  // set the output for the current iteration to zeros. used for short sequence lengths
   void ZeroOutCurrent() {
     auto* tensor = (**this).GetMutable<Tensor>();
     memset(tensor->MutableDataRaw(), 0, tensor->Size());
@@ -160,7 +163,10 @@ class OutputIterator {
   int64_t num_iterations_;
   int64_t cur_iteration_;
 
+  // is the final shape concrete, or does it have symbolic dimensions
   bool is_concrete_shape_;
+
+  // one or more slicers for writing to the output
   std::vector<MLValueTensorSlicer<MLValue>::Iterator> slicer_iterators_;
   std::vector<MLValueTensorSlicer<MLValue>::Iterator>::iterator cur_slicer_iterator_;
 
@@ -302,6 +308,7 @@ void LoopStateVariable::Next() {
   ++iteration_num_;
 }
 
+// fill in a symbolic dimension in the overall output using the output shape from an iteration of the subgraph
 static Status MakeShapeConcrete(const TensorShape& per_iteration_shape, TensorShape& final_shape) {
   auto num_dims_per_iteration = per_iteration_shape.NumDimensions();
   auto final_shape_offset = final_shape.NumDimensions() - num_dims_per_iteration;