created: 20140925190154910
modified: 20141021175913459
tags: Terminology
title: Shadow Tiddler
type: text/vnd.tiddlywiki

!Abstract

<<imagethumb "ThirdFlow Architecture Tiddler Terms.jpg" "50%">>

A ''shadow tiddler'' in ~TiddlyWiki 5 is a tiddler that originates from a [[plugin|Plugin]]. Shadow tiddlers cannot be changed, but they can be overwritten  simply by creating a new tiddler (so-called [[ordinary tiddlers|Ordinary Tiddler]]) with the same name.

For lack of a better name, I'll call (ordinary) tiddlers overwriting shadows the [[foreground tiddlers|Foreground Tiddler]]. If an ordinary tiddler has a shadow, then the ordinary is the foreground one. Otherwise, I stick to the established term of ordinary tiddler.

!Technical

Internally, the ~TiddlyWiki 5 core stores shadow tiddlers in its own tiddler table that is ''separate'' from the ordinary tiddler table. This is crucial to understand, as this has some important ramifications:

* iterations over ordinary and shadow tiddlers are clearly separate.
* the JavaScript objects for ordinary tiddlers and shadow tiddlers differ:
** you can create and delete ordinary tiddlers (that is, adding or removing them to/from the tiddler store using `$tw.wiki.addTiddler()` and `$tw.wiki.removeTiddler()`), but you can't do so directly for shadown tiddlers.
** ordinary tiddler objects have a `fields` element that is a hashmap of the fields of a tiddler.

The shadow tiddler table only gets populated when [[plugins|Plugin]] are unpacked: either during boot or when importing them later.

!See Also

* [[Ordinary Tiddler]] -- the one that //isn't// a shadow.
* [[Foreground Tiddler]] -- the one that //has// a shadow.
* [[shadowinsync is Filter Operand]] -- checks for shadows that are in sync with their foregrounds.