diff --git a/src/smeagol/extensions/vega.clj b/src/smeagol/extensions/vega.clj
index e69de29..14cf285 100644
--- a/src/smeagol/extensions/vega.clj
+++ b/src/smeagol/extensions/vega.clj
@@ -0,0 +1,84 @@
+(ns ^{:doc "Format Semagol's extended markdown format."
+      :author "Simon Brooke"}
+  smeagol.extensions.vega
+  (:require [smeagol.extensions.utils :refer :all]
+            [taoensso.timbre :as log]))
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;;;;
+;;;; Smeagol: a very simple Wiki engine.
+;;;;
+;;;; This program is free software; you can redistribute it and/or
+;;;; modify it under the terms of the GNU General Public License
+;;;; as published by the Free Software Foundation; either version 2
+;;;; of the License, or (at your option) any later version.
+;;;;
+;;;; This program is distributed in the hope that it will be useful,
+;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;;; GNU General Public License for more details.
+;;;;
+;;;; You should have received a copy of the GNU General Public License
+;;;; along with this program; if not, write to the Free Software
+;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301,
+;;;; USA.
+;;;;
+;;;; Copyright (C) 2017 Simon Brooke
+;;;;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;;;;
+;;;; Inspired by [visdown](https://visdown.com/) and
+;;;; [vega-lite](https://vega.github.io/vega-lite/docs/), the Vega formatter
+;;;; allows you to embed vega data visualisations into Smeagol pages. The graph
+;;;; description should start with a line comprising three back-ticks and then
+;;;; the word '`vega`', and end with a line comprising just three backticks.
+;;;;
+;;;; Here's an example cribbed in its entirety from
+;;;; [here](http://visdown.amitkaps.com/london):
+;;;;
+;;;; ### Flight punctuality at London airports
+;;;;
+;;;; ```vega
+;;;; data:
+;;;;   url: "data/london.csv"
+;;;; transform:
+;;;;  -
+;;;;   filter: datum.year == 2016
+;;;; mark: rect
+;;;; encoding:
+;;;;   x:
+;;;;     type: nominal
+;;;;     field: source
+;;;;   y:
+;;;;     type: nominal
+;;;;     field: dest
+;;;;   color:
+;;;;     type: quantitative
+;;;;     field: flights
+;;;;     aggregate: sum
+;;;; ```
+;;;;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(defn process-vega
+  "If this `src-resource-or-url` is a valid URL, it is assumed to point to a
+  plain text file pointing to  valid `vega-src`; otherwise, it is expected to
+  BE a valid `vega-src`.
+
+  Process this `vega-src` string, assumed to be in YAML format, into a
+  specification of a Vega chart, and add the plumbing to render it."
+  [^String src-resource-or-url ^Integer index]
+  (let [data (resource-url-or-data->data url-or-graph-spec)
+        vega-src (:data data)]
+    (log/info "Retrieved vega-src from " (:from data) " `" ((:from data) data) "`")
+    (str
+      "<div class='data-visualisation' id='vis" index "'></div>\n"
+      "<script>\n//<![CDATA[\nvar vl"
+      index
+      " = "
+      (yaml->json (str "$schema: https://vega.github.io/schema/vega-lite/v2.json\n" vega-src))
+      ";\nvegaEmbed('#vis"
+      index
+      "', vl"
+      index
+      ");\n//]]\n</script>")))