Add doc for Scratch

docs/content/extras/pagination.md

@@ -5,7 +5,7 @@ date: 2014-01-01
 menu:
   main:
     parent: extras
-next: /extras/highlighting
+next: /extras/scratch
 prev: /extras/shortcodes
 title: Pagination
 weight: 80

docs/content/extras/scratch.md

@@ -0,0 +1,42 @@
+---
+aliases:
+- /doc/scratch/
+date: 2015-01-22
+menu:
+  main:
+    parent: extras
+next: /extras/highlighting
+prev: /extras/pagination
+title: Scratch
+weight: 80
+---
+
+`Scratch` -- a "scratchpad" for your node- or page-scoped variables. In most cases you can do well without `Scratch`, but there are some use cases that aren't solvable with Go's templates without `Scratch`'s help, due to scoping issues.
+
+
+`Scratch` is added to both `Node` and `Page` -- with the three methods `Set`, `Get` and `Add`. `Set` and `Add` takes a `key` and the `value` to add. Get returns the `value` for the `key` given.
+
+`Set` can store values of any type. `Add` accepts values that support Go's `+` operator.
+
+The scope of the backing data is global for the given `Node` or `Page`, and spans partial and shortcode includes.
+
+## Sample usage
+
+The usage is best illustrated with some samples:
+
+```
+{{ .Scratch.Add "a1" 12 }}
+{{ .Scratch.Get "a1" }} {{/* => 12 */}}
+{{ .Scratch.Add "a1" 1 }}
+{{ .Scratch.Get "a1" }} // {{/* => 13 */}}
+
+{{ .Scratch.Add "a2" "AB" }}
+{{ .Scratch.Get "a2" }} {{/* => AB */}}
+{{ .Scratch.Add "a2" "CD" }}
+{{ .Scratch.Get "a2" }} {{/* => ABCD */}}
+
+{{ .Scratch.Set "v1" 123 }}
+{{ .Scratch.Get "v1" }}  {{/* => 123 */}}       
+```
+
+