diff --git a/src/re_demo/nested_grid.cljs b/src/re_demo/nested_grid.cljs
index af58233e..30dc9239 100644
--- a/src/re_demo/nested_grid.cljs
+++ b/src/re_demo/nested_grid.cljs
@@ -1,8 +1,10 @@
 (ns re-demo.nested-grid
-  (:require [re-com.core   :as rc :refer [at h-box v-box box gap line label p p-span hyperlink-href]]
-            [reagent.core :as r]
-            [re-com.nested-grid  :as nested-grid :refer [nested-grid nested-grid-args-desc nested-grid-parts-desc]]
-            [re-demo.utils :refer [source-reference panel-title title2 title3 args-table parts-table github-hyperlink status-text new-in-version]]))
+  (:require
+   [clojure.string :as str]
+   [re-com.core   :as rc :refer [at h-box v-box box gap line label p p-span hyperlink-href]]
+   [reagent.core :as r]
+   [re-com.nested-grid  :as nested-grid :refer [nested-grid nested-grid-args-desc nested-grid-parts-desc]]
+   [re-demo.utils :refer [source-reference panel-title title2 title3 args-table parts-table github-hyperlink status-text new-in-version]]))
 
 (def arg-style {:style {:display     "inline-block"
                         :font-weight "bold"
@@ -39,7 +41,7 @@
    "darkyellow"  "gold"})
 
 (defn mix-colors [color1 color2]
-  (name (get-in color-mixer [color1 color2])))
+  (name (get-in color-mixer [(keyword color1) (keyword color2)])))
 
 (mix-colors :red :yellow)
 
@@ -48,21 +50,21 @@
    :children
    [[p "Here's a grid with flat columns and rows."
      " The " [:code ":cell"] " function closes over some external business logic ("
-     [:code "mix-colors"] ") to express a string value."
+     [:code "mix-colors"] ") to express a string."
      " Since there is only one level of nesting, " [:code "column-path"]
-     " contains a single " [:code "column"] " value - for instance, "
+     " contains a single " [:i "header value"] " - for instance, "
      [:code "[:red]"] "."]
     [:pre "[nested-grid
- :columns [:red :yellow :blue]
- :rows    [:red :yellow :blue]
+ :columns [\"red\" \"yellow\" \"blue\"]
+ :rows    [\"red\" \"yellow\" \"blue\"]
  :cell    (fn color-cell [{:keys [column-path row-path]}]
              (mix-colors (last column-path)
                          (last row-path)))]"]]])
 
 (defn color-demo []
   [nested-grid
-   :columns [:red :yellow :blue]
-   :rows    [:red :yellow :blue]
+   :columns ["red" "yellow" "blue"]
+   :rows    ["red" "yellow" "blue"]
    :cell    (fn color-cell [{:keys [row-path column-path]}]
               (mix-colors (last row-path)
                           (last column-path)))])
@@ -70,7 +72,8 @@
 (defn color-shade-explainer []
   [rc/v-box
    :children
-   [[p "Since " [:code ":columns"] " is a vector tree with 2 levels of nesting,"
+   [[p "Here, " [:code ":columns"] "is a nested " [:i "configuration"] " of " [:i "header values."]]
+    [p "Since the " [:i "configuration"] " has 2 levels of nesting,"
      " each " [:code ":column-path"] " is 2-long. For instance, "
      [:code "[:medium :yellow]"] ". "]
     [p [:code ":cell"] " returns a hiccup."]
@@ -78,11 +81,11 @@
      "should return a " [:span {:style {:color "green"}} "green"] " hiccup."]
 
     [:pre "[nested-grid
-   {:columns [:medium [:red :yellow :blue]
-              :light  [:red :yellow :blue]
-              :dark   [:red :yellow :blue]]
-    :rows    [:red :yellow :blue]
-    :cell    color-shade-cell}]"]]])
+   :columns [:medium [:red :yellow :blue]
+             :light  [:red :yellow :blue]
+             :dark   [:red :yellow :blue]]
+   :rows    [:red :yellow :blue]
+   :cell    color-shade-cell]"]]])
 
 (defn color-shade-cell [{:keys [row-path column-path]}]
   (let [[row-hue]       row-path
@@ -133,7 +136,7 @@
 
 (def lookup-table [["🚓" "🛵" "🚲" "🛻" "🚚"]
                    ["🍐" "🍎" "🍌" "🥝" "🍇"]
-                   ["🐈" "🐕" "🐟" "🐎" "🧸"]])
+                   ["🐕" "🐎" "🧸" "🐈" "🐟"]])
 
 (def add {:operator + :label "Addition"})
 (def multiply {:operator * :label "Multiplication"})
@@ -157,96 +160,91 @@
     [title3 "Cells are Functions"]
     [p "Each cell is a " [:i "function"] " of its grid position."]
     [nested-grid
-     :columns [:a :b :c]
-     :rows    [:x :y :z]
+     :columns ["a" "b" "c"]
+     :rows    ["x" "y" "z"]
      :column-width 40
      :column-header-height 25
      :row-header-width 30
-     :cell    (fn [{:keys [column-path row-path]}] (pr-str (concat column-path row-path)))]
+     :cell    (fn [{:keys [column-path row-path]}]
+                (str "(" (last column-path)
+                     ", " (last row-path) ")"))]
     [title3 "Headers are Nested"]
-    [p "You can declare a tree of nested header values. "]
+    [p "You can declare headers as a nested " [:i "configuration."]]
     [nested-grid
      :columns [:a [:a1 :a2] :b [:b1 :b2]]
      :rows    [:x [:x1 :x2] :y [:y1 :y2]]
      :column-header-height 25
      :row-header-width 30
      :column-width 90
-     :cell    (fn [{:keys [column-path row-path]}]
-                (pr-str (list column-path row-path)))]
-    [p [:code ":columns"] " is a tree of nested " [:code "column"] " values. For instance: "]
-    [:pre ":columns [:a [:a1 :a2] :b [:b1 :b2]]
-:rows    [:x [:x1 :x2] :y [:y1 :y2]]"]
-    [p "That means each vertical partition you see is defined by a " [:code ":column-path"]
-     "(not simply a " [:code "column"] "). "
+     :cell    (comp str seq (juxt :column-path :row-path))]
+    [p "Each vertical partition you see is defined by a " [:code ":column-path"] "."
      "For instance, " [:code "[:a :a1]"] " is the first " [:code ":column-path"] "."]
     [p "Same goes for rows. For instance, " [:code "[:y :y2]"] " is the last " [:code ":row-path"] "."]
-    [title3 "Headers can be Richly Declarative"]
-
-    [p "A " [:code ":column-path"] " is a vector of " [:code "column"] " values."]
-
-    [p "Anything can be a " [:code "column"] " value, "
-     [:i "except"] " a " [:code "list"] " or " [:code "vector"] " (those express nesting)."]
-
-    [nested-grid
-     :columns [add      [one two]
-               multiply [one two]
-               lookup   [one two]]
-     :rows    [three four]
-     :row-header (comp :label last :row-path)
-     :column-header (comp :label last :column-path)
-     :row-header 20
-     :column-header-height 25
-     :row-header-width 100
-     :parts {:cell-wrapper {:style {:text-align "center"}}}
-     :cell    (fn [{:keys [column-path row-path]}]
-                (let [{:keys [operator left right]} (->> (into row-path column-path)
-                                                         (apply merge))]
-                  (operator left right)))]
-    [:pre "(def lookup-table [[\"🚓\" \"🛵\" \"🚲\" \"🛻\" \"🚚\"]
-                   [\"🍐\" \"🍎\" \"🍌\" \"🥝\" \"🍇\"]
-                   [\"🐈\" \"🐕\" \"🐟\" \"🐎\" \"🧸\"]])
-(def add      {:operator + :label \"Addition\"})
-(def multiply {:operator * :label \"Multiplication\"})
-(def lookup   {:operator (fn [l r] (get-in lookup-table [l r]))
-               :label    \"Lookup\"})
-(def one      {:left 1 :label \"1\"})
-(def two      {:left 2 :label \"2\"})
-(def three    {:right 3 :label \" 3 \"})
-(def four     {:right 4 :label \" 4 \"})
-
-[nested-grid
- :columns       [add      [one two]
-                 multiply [one two]
-                 lookup   [one two]]
- :rows          [three four]
- :column-header (comp :label last :column-path)
- :row-header    (comp :label last :row-path)
- :cell          (fn [{:keys [column-path row-path]}]
-                  (let [{:keys [operator left right]} (->> column-path
-                                                           (into row-path)
-                                                           (apply merge))]
-                    (operator left right)))]"]
-    [title3 "Header Cells are Functions"]
+    [title3 "Cells are Views of Header Paths"]
+    [p "Each cell is a function of its location."]
+    [h-box
+     :gap "25px"
+     :children
+     [[nested-grid
+       :columns [:a :b :c]
+       :rows    [:x [:x1 :x2]
+                 :y [:y1 :y2]]
+       :column-width 70
+       :column-header-height 25
+       :row-header-width 30
+       :cell    (fn [{:keys [column-path row-path]}]
+                  [:i (str (list column-path row-path))])]
+      [v-box
+       :children
+       [[gap :size "20px"]
+        [:pre "[nested-grid
+ :columns [:a :b :c]
+ :rows    [:x [:x1 :x2]
+           :y [:y1 :y2]]
+ :cell
+ (fn [{:keys [column-path row-path]}]
+   [:i (str (list column-path row-path))])]"]]]]]
+    [p "Specifically, the " [:code ":cell"] " prop accepts a function "
+     "of two keyword arguments: " [:code ":column-path"] " and " [:code ":row-path"] "."]
+    [p "The function counts as a "
+     [:a {:href "https://github.com/reagent-project/reagent/blob/master/doc/CreatingReagentComponents.md"}
+      "reagent component"] ", returning either a string or a hiccup."]
+    [title3 "Header Cells are Views, Too"]
     [p "Just like " [:code ":cell"] ", the " [:code ":column-header"] " and " [:code ":row-header"] " props "
-     "are functions of paths."]
+     "are functions of their location."]
     [p "The difference is, a " [:code ":column-header"] " only has a " [:code ":column-path"]
      " and a " [:code ":row-header"] " only has a " [:code ":row-path"] "."]
+    [title3 "Headers are Richly Declarative"]
+    [p "A " [:code ":column-path"] " is a vector of " [:i "header values."]]
+    [p "Anything can be a " [:i "header value"] ", "
+     [:i "except"] " a " [:code "list"] " or " [:code "vector"] " (those express " [:i "configuration"] ")."]
+    [p "So far, we've looked at simple " [:i "header values"] ", like " [:code ":a"] " or " [:code "\"blue\""] "."]
+    [p "Another common use-case is a map, like " [:code "{:id :a :label \"A\" :type :letter}"] "."
+     "We consider a value like this to be a " [:i "header spec"] "."]
     [title3 "Nested-grid + Domain Logic = Pivot Table"]
-    [:i {:style {:max-width "400px"}} "A pivot table is a table of values which are aggregations of groups of individual values from a more extensive table...  within one or more discrete categories. (" [:a {:href "https://en.wikipedia.org/wiki/Pivot_table"} "Wikipedia"] ")"]
+    [:i {:style {:max-width "400px"}}
+     "A pivot table is a table of values which are aggregations of groups of individual values from a more extensive table..."
+     "within one or more discrete categories. (" [:a {:href "https://en.wikipedia.org/wiki/Pivot_table"} "Wikipedia"] ")"]
     [:br]
     [p "The pivot table is our driving use-case. "
      "By separating UI presentation from data presentation, we hope "
      [:code "nested-grid"] " makes it simple to build robust and flexible pivot tables."]
-    [p "In particular, your " [:code ":cell"] " function can close over concepts like " [:i "aggregations, groups, categories, dimensions, measures,"] " etc."]
-    [p "In the example above, " [:code "lookup-table"] "demonstrates the concept of "
-     [:i "a more extensive table."]
-     " Your " [:code ":columns"] " and " [:code ":rows"]
-     " can declare the necessary domain concepts, and your " [:code ":cell"] " function can dispatch on each concept, "
-     "accessing various " [:i "aggregations"] " and " [:i "groupings"] " of that table."]
+    [p "In " [:strong "Demo #3: Header Specifications"] ", " [:code "lookup-table"] "declares "
+     [:i "\"a more extensive table,\""]
+     " and the " [:code "lookup"] [:i "column spec"] " declares how to use that table."]
+    [p
+     "More generally:" [:br]
+     [:ul
+      [:li "Your " [:code ":columns"] " and " [:code ":rows"]
+       " declare the necessary domain concepts, such as "
+       [:i "\"aggregations\""] " and " [:i "\"groups.\""]]
+      [:li "Your " [:code ":cell"] " function dispatches on each concept, "
+       "deriving these " [:i "\"aggregations\""] " and " [:i "\"groups\""] " from "
+       [:i "\"a more extensive table.\""]]]]
     [p "We also envision building an interactive, configurable pivot table. "
-     "By changing the value of " [:code ":columns"] " and " [:code ":rows"] ", you can reconfigure the UI presentation, and "
-     "your data presentation can simply follow along. "
-     "This can be done either programmatically or via a dedicated user interface."]]])
+     "By changing " [:code ":columns"] " and " [:code ":rows"] ", you could reconfigure the UI presentation, and "
+     "your data presentation would simply follow along. "
+     "This could be done either programmatically or via a dedicated user interface."]]])
 
 ;; core holds a reference to panel, so need one level of indirection to get figwheel updates
 (defn panel
@@ -285,7 +283,7 @@
           [v-box
            :src      (at)
            :children
-           [[title2 "Demo #1"]
+           [[title2 "Demo #1: Flat Headers"]
             [gap
              :src      (at)
              :size "15px"]
@@ -298,7 +296,7 @@
              :src      (at)
              :size "40px"]
             [line :src      (at)]
-            [title2 "Demo #2"]
+            [title2 "Demo #2: Nested Headers"]
             [gap
              :src      (at)
              :size "15px"]
@@ -306,5 +304,50 @@
             [source-reference
              "for above nested-grid"
              "src/re_demo/nested_grid.cljs"]
-            [color-shade-explainer]]]]]
+            [color-shade-explainer]
+            [title2 "Demo #3: Header Specifications"]
+            [nested-grid
+             :columns [add      [one two]
+                       multiply [one two]
+                       lookup   [one two]]
+             :rows    [three four]
+             :row-header (comp :label last :row-path)
+             :column-header (comp :label last :column-path)
+             :row-header 20
+             :column-header-height 25
+             :row-header-width 100
+             :parts {:cell-wrapper {:style {:text-align "center"}}}
+             :cell    (fn [{:keys [column-path row-path]}]
+                        (let [{:keys [operator left right]} (->> (into row-path column-path)
+                                                                 (apply merge))]
+                          (operator left right)))]
+            [source-reference
+             "for above nested-grid"
+             "src/re_demo/nested_grid.cljs"]
+            [p "Here, we use " [:i "header specs"] " like " [:code "multiply"]
+             " and " [:code "lookup"] " to build a multi-modal view of the source data."]
+            [:pre "(def lookup-table [[\"🚓\" \"🛵\" \"🚲\" \"🛻\" \"🚚\"]
+                   [\"🍐\" \"🍎\" \"🍌\" \"🥝\" \"🍇\"]
+                   [\"🐕\" \"🐎\" \"🧸\" \"🐈\" \"🐟\"]])
+(def add      {:label \"Addition\"       :operator +})
+(def multiply {:label \"Multiplication\" :operator *})
+(def lookup   {:label \"Lookup\"
+               :operator (fn [l r] (get-in lookup-table [l r]))})
+(def one      {:label \"1\" :left 1})
+(def two      {:label \"2\" :left 2})
+(def three    {:label \"3\" :right 3})
+(def four     {:label \"4\" :right 4})
+
+[nested-grid
+ :columns       [add      [one two]
+                 multiply [one two]
+                 lookup   [one two]]
+ :rows          [three four]
+ :column-header (comp :label last :column-path)
+ :row-header    (comp :label last :row-path)
+ :cell          (fn [{:keys [column-path row-path]}]
+                  (let [{:keys [operator left right]} (->> column-path
+                                                           (into row-path)
+                                                           (apply merge))]
+                    (operator left right)))]"]]]]]
         #_[parts-table "nested-grid" nested-grid-grid-parts-desc]]])))