diff --git a/main/src/com/google/refine/importers/tree/ImportColumn.java b/main/src/com/google/refine/importers/tree/ImportColumn.java
index ec07a7ca4..4bc7898ea 100644
--- a/main/src/com/google/refine/importers/tree/ImportColumn.java
+++ b/main/src/com/google/refine/importers/tree/ImportColumn.java
@@ -6,8 +6,17 @@ package com.google.refine.importers.tree;
  *
  */
 public class ImportColumn extends ImportVertical {
+    /**
+     * Index of this column.
+     */
     public int      cellIndex;
-    public int      nextRowIndex;
+    /**
+     * Index of next row to allocate.
+     */
+    public int      nextRowIndex;  // TODO: this can be hoisted into superclass
+    /**
+     * ??? - this field is never written to
+     */
     public boolean  blankOnFirstRow;
 
     public ImportColumn() {}
@@ -18,6 +27,6 @@ public class ImportColumn extends ImportVertical {
 
     @Override
     void tabulate() {
-        // already done the tabulation elsewhere
+        // Nothing to do since our nonBlankCount is always up-to-date and we have no children.
     }
 }
\ No newline at end of file
diff --git a/main/src/com/google/refine/importers/tree/ImportColumnGroup.java b/main/src/com/google/refine/importers/tree/ImportColumnGroup.java
index d50e2838d..233ac0da2 100644
--- a/main/src/com/google/refine/importers/tree/ImportColumnGroup.java
+++ b/main/src/com/google/refine/importers/tree/ImportColumnGroup.java
@@ -11,7 +11,7 @@ import org.apache.commons.lang.StringUtils;
 public class ImportColumnGroup extends ImportVertical {
     public Map<String, ImportColumnGroup> subgroups = new HashMap<String, ImportColumnGroup>();
     public Map<String, ImportColumn> columns = new HashMap<String, ImportColumn>();
-    public int nextRowIndex;
+    public int nextRowIndex; // TODO: this can be hoisted into superclass
 
     @Override
     void tabulate() {
diff --git a/main/src/com/google/refine/importers/tree/ImportVertical.java b/main/src/com/google/refine/importers/tree/ImportVertical.java
index 0a29e8d75..58524bfd4 100644
--- a/main/src/com/google/refine/importers/tree/ImportVertical.java
+++ b/main/src/com/google/refine/importers/tree/ImportVertical.java
@@ -1,9 +1,18 @@
 package com.google.refine.importers.tree;
 
+/**
+ * Abstract base class for ImportColumn and ImportColumnGroup
+ */
 abstract class ImportVertical {
     public String name = "";
+    /**
+     * Number of cells which have values in this column/column group.
+     */
     public int nonBlankCount;
 
+    /**
+     * Sum up counts for all children and update.
+     */
     abstract void tabulate();
     
     @Override