Update template documentation to include DataList methods

https://github.com/silverstripe/sapphire/pull/1799.

docs/en/reference/templates.md

@@ -217,6 +217,9 @@ collection of items. For example:
 This loops over the children of a page, and generates an unordered list showing
 the `Title` property from each one. Note that `$Title` *inside* the loop refers
 to the `Title` property on each object that is looped over, not the current page.
+This is know as the `Scope` of the template. For more information about `Scope`
+see the section below.
+
 To refer to the current page's `Title` property inside the loop, you can do
 `$Up.Title`. More about `Up` later.
 
@@ -235,6 +238,50 @@ current position in the list and iteration:
  * `$Pos`: The current position in the list (integer). Will start at 1.
  * `$TotalItems`: Number of items in the list (integer)
 
+### Altering the list
+
+`<% loop %>` statements iterate over a `[api:DataList]` instance. As the
+template has access to the list object, templates can call `[api:DataList]`
+functions. For instance, see the following examples:
+
+Providing a custom sort.
+
+	:::ss
+	<ul>
+		<% loop $Children.Sort(Title) %>
+			<li>$Title</li>
+		<% end_loop %>
+	</ul>
+
+Limiting the number of items displayed.
+
+	:::ss
+	<ul>
+		<% loop $Children.Limit(10) %>
+			<li>$Title</li>
+		<% end_loop %>
+	</ul>
+
+Reversing the loop.
+
+	:::ss
+	<ul>
+		<% loop $Children.Reverse %>
+			<li>$Title</li>
+		<% end_loop %>
+	</ul>
+
+
+The `DataList` class also supports chaining methods. For example, to reverse
+the list and output the last 3 items we would write:
+
+	:::ss
+	<ul>
+		<% loop $Children.Reverse.Limit(3) %>
+			<li>$Title</li>
+		<% end_loop %>
+	</ul>
+
 ### Modulus and MultipleOf
 
 $Modulus and $MultipleOf can help to build column layouts.