Here we provide an overview of those mechanisms and how they relate together.
!! Special Fields
Special fields are used to assign an appearance or behaviour to individual tiddlers. They can be thought of as flags or values that directly control the tiddler to which they are applied.
For example:
* Set the `icon` field to the title of an image tiddler to be used as the icon for this tiddler
* Set the `color` field to a CSS colour that is then used for icons and tag pills associated with this tiddler
* Set the `hide-body` field to `yes` to hide the view template body for this tiddler
See TiddlerFields for details of all the special fields.
!! Special Titles
Certain special titles identify configuration tiddlers that customise TiddlyWiki's appearance or behaviour. They can be thought of as global settings that affect an entire wiki.
For example:
* $:/DefaultTiddlers is a filter yielding the titles of the tiddlers that should be displayed at startup
* $:/SiteTitle specifies the text of the wiki title
* $:/config/Tags/MinLength controls the minimum number of characters to trigger tag autocompletion
Many of TiddlyWiki's configuration tiddlers are presented as options in [[$:/ControlPanel]]. Less commonly used configuration tiddlers do not have a user interface, but are documented in [[Hidden Settings]].
!! Special Tags
Special tags assign special behaviour or appearance to all of the tiddlers to which they are applied. They can be thought of as establishing ordered lists of tiddlers that are processed or displayed in a particular way.
* $:/tags/Stylesheet causes the tiddler to be interpreted as a CSS stylesheet
* $:/tags/SideBar causes the tiddler to be displayed as a sidebar tab
See SystemTags for details of all the special tags.
The entire TiddlyWiki user interface is constructed from lists formed from special system tags.
The ordering of these lists is determined by the [[order of tagged tiddlers|Order of Tagged Tiddlers]] rules. Users can re-order tags using drag and drop within a tag dropdown.
Cascades provide a means to select one of multiple values based on flexible, extensible criteria. They can be thought of as a list of conditions that are evaluated in turn until one of them matches.
For example, the core uses the template $:/core/ui/ViewTemplate to display tiddlers in view mode, and $:/core/ui/EditTemplate to display tiddlers in edit mode. A cascade is used to choose which template to use for a particular tiddler:
# If the tiddler is a draft, then use $:/core/ui/EditTemplate
The list of conditions is defined via a special tag, making it possible to insert additional conditions anywhere in the list.
For example, a plugin might add a special template $:/plugins/example/map-template for tiddlers that have the tag [[$:/tags/Map]] by inserting an additional rule:
# If the tiddler is a draft, then use $:/core/ui/EditTemplate
# @@background: yellow; If the tiddler is tagged $:/tags/Map, then use $:/plugins/example/map-template@@
