diff --git a/docs/src/index.md b/docs/src/index.md
index 565dc6c..95c2e8e 100644
--- a/docs/src/index.md
+++ b/docs/src/index.md
@@ -63,7 +63,7 @@ The definition of orthogonal forms for MPOs or operator-valued matrices are more
 ```math
 \sum_{a}\left\langle \hat{W}_{ab}^{\dagger},\hat{W}_{ac}\right\rangle =\frac{\sum_{a}^{}Tr\left[\hat{W}_{ab}\hat{W}_{ac}\right]}{Tr\left[\hat{\mathbb{I}}\right]}=\delta_{bc}
 ```
-Where the summation limits depend on where the V-block is for `left`/`right` and `lower`/`upper`.  The specifics for all four cases are shown in table 6 in the [Technical Notes](../TechnicalDetails.pdf)
+Where the summation limits depend on where the V-block is for `left`/`right` and `lower`/`upper`.  The specifics for all four cases are shown in table 6 in the [Technical Notes](https://github.com/JanReimers/ITensorMPOCompression.jl/blob/main/docs/TechnicalDetails.pdf)
 
 ```@docs
 ITensorMPOCompression.orth_type
@@ -85,3 +85,11 @@ MPOs for various models.  Right now we have four Hamiltonians available
 4. The 3-body model in eq. 34 of the Parker paper, built with autoMPO.
 The autoMPO MPOs come pre-truncated so they are not as useful for testing truncation. The automated truncation in AutoMPO can **partially** disabled by providing the the keyword argument `cutoff=-1.0` which gets passed down in the svd/truncate call used when building the MPO
 
+# Internal structures
+
+Internally the orthogonalization and truncation code uses these structures for storing and manipulating MPOs and matrix operators: Ŵ.
+
+```@docs
+reg_form_Op
+reg_form_MPO
+```
diff --git a/src/ITensorMPOCompression.jl b/src/ITensorMPOCompression.jl
index ef2de9f..e7aa2cd 100644
--- a/src/ITensorMPOCompression.jl
+++ b/src/ITensorMPOCompression.jl
@@ -26,7 +26,7 @@ export bond_spectrums
 # Display helpers
 export @pprint, pprint, show_directions
 # Wrapped MPO types
-export reg_form_MPO
+export reg_form_Op, reg_form_MPO
 
 macro mpoc_assert(ex)
   esc(:($Base.@assert $ex))
diff --git a/src/reg_form_MPO.jl b/src/reg_form_MPO.jl
index d5aed56..6848d67 100644
--- a/src/reg_form_MPO.jl
+++ b/src/reg_form_MPO.jl
@@ -1,9 +1,21 @@
-#-----------------------------------------------------------------------
-#
-#  Finite lattice with open BCs, of regulat form Tensos: l*W1*W2...*WN*r
-#  Edge tensors have dim=1 dummy indices (order(W)==4) so generic code can work the same
-#  on all tensors.
-#
+@doc """
+  `mutable struct reg_form_MPO <: AbstractMPS` 
+
+# Fields
+- `data`::`Vector{reg_form_Op}` string of order 4 operators Ŵ
+- `llim`::`Int64`               One site left of ortho center
+- `rlim`::`Int64`               One site right of ortho center
+- `d0`  ::`ITensor`             onehot tensor used to add a dummy, dim=1  index at the left  edge of the `MPO`
+- `dN`  ::`ITensor`             onehot tensor used to add a dummy, dim=1 index at the right edge of the `MPO`
+- `ul`  ::`reg_form`            Flag indicating {`lower`,`upper`} regular form.
+    
+# Description
+  Finite lattice with open boundary condicitions, of regular form Tensors: l*Ŵ₁*Ŵ₂...*Ŵₙ*r
+  Edge tensors have dim=1 dummy indices (so that order(Ŵ)==4) so generic code can work the same 
+  on all tensors.  `d0` and `dN` are stored and used later to remove the dummy indices when converting back to an `MPO`. 
+  Dummy indices are created, and  `lower`/`upper` detection is performed at construction time. 
+    
+"""
 mutable struct reg_form_MPO <: AbstractMPS
     data::Vector{reg_form_Op}
     llim::Int # orthocenter-1
diff --git a/src/reg_form_Op.jl b/src/reg_form_Op.jl
index 826c19c..65708cc 100644
--- a/src/reg_form_Op.jl
+++ b/src/reg_form_Op.jl
@@ -2,8 +2,25 @@
 #
 #  Manage an MPO/iMPO tensor and track the left and right facing indices.  This 
 #  seems to be easiest way to avoid tag hunting.  
-#  Also track lower or upper regular form in ul member.
+#  Also track lower or upper regular form in ul member. 
 #
+@doc """
+`mutable struct reg_form_Op`
+
+# Fields
+- `W::ITensor`    Order 4 four operator valued matrix: Ŵ    
+- `ileft::Index`  Left facing link index
+- `iright::Index` Right facing link index
+- `ul::reg_form`  Flag indicating {upper,lower} regular form
+
+# Description
+During construction the data in `W` is interrogated once to confirm either upper or lower regular form.  Similarly for
+the left and right link indices, except that various function overloads may automatically update the indices as needed.
+This appraoch greatly simplifies all the orthogonalization and truncation code which needs to know `ileft` and `iright` at almost
+every step.
+        
+
+"""
 mutable struct reg_form_Op
     W::ITensor
     ileft::Index
@@ -11,14 +28,14 @@ mutable struct reg_form_Op
     ul::reg_form
     function reg_form_Op(W::ITensor, ileft::Index, iright::Index, ul::reg_form)
         if !hasinds(W, ileft, iright)
-        @show inds(W, tags="Link") ileft iright
+            @show inds(W, tags="Link") ileft iright
         end
         @assert hasinds(W, ileft, iright)
         return new(W, ileft, iright, ul)
     end
-    function reg_form_Op(W::ITensor, ul::reg_form)
-        return new(W, Index(1), Index(1), ul)
-    end
+    # function reg_form_Op(W::ITensor, ul::reg_form)
+    #     return new(W, Index(1), Index(1), ul)
+    # end
 end
 #
 #  Internal consistency checks