Move docs for 5.1.5 release

editions/tw5.com/tiddlers/widgets/SetWidget.tid

@@ -1,6 +1,6 @@
 title: SetWidget
 created: 201311151827
-modified: 201311151827
+modified: 20141113212520422
 tags: Widgets
 caption: set
 
@@ -13,5 +13,45 @@ The set variable widget assigns a value to a specified [[variable|WidgetVariable
 The content of the `<$set>` widget is the scope for the value assigned to the variable.
 
 |!Attribute |!Description |
-|name |The name of the variable to assign |
-|value |The value to assign to the variable |
+|name |The name of the variable to assign (defaults to "currentTiddler") |
+|value |The value to assign to the variable if the filter is missing or not empty |
+|filter |An optional filter to be evaluated and assigned to the variable (see below) |
+|emptyValue |The value to assign to the variable if the filter is present and evaluates to an empty list (see below) |
+
+!! Simple Variable Assignment
+
+The simplest way of using set variable widget assigns a string to a variable. The following example assigns a literal string
+
+```
+<$set name="myVariable" value="Some text">
+<$text text=<<myVariable>>/>
+</$set>
+```
+
+Both the name and value attributes can be transcluded. For example:
+
+```
+<$set name=<<anotherVariable>> value={{template!!text}}>
+<$text text=<<myVariable>>/>
+</$set>
+```
+
+!! Conditional Variable Assignment
+
+This form of the set variable widget chooses one of two specified values according to whether a filter evaluates to an empty list. Here's an example that sets a variable according to whether the current tiddler is called "myMagicTitle":
+
+```
+<$set name="myVariable" filter="[all[current]field:title[myMagicTitle]]" value="It's magic" emptyValue="It's not magic">
+<$text text=<<myVariable>>/>
+</$set>
+```
+
+!! Filtered List Variable Assignment
+
+This form of the set variable widget evaluates the filter and assigns the result to the variable as a space-separated list (using double square brackets for titles containing spaces).
+
+```
+<$set name="myVariable" filter="[tag[Introduction]]">
+<$text text=<<myVariable>>/>
+</$set>
+```