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Transclusion with Templates

20th February 2015 at 4:14pm
Transclusion in WikiText

Introduction

In Transclusion Basic Usage we have seen how to include the content of a tiddler A into a tiddler B. Now suppose that tiddler A contains:

@@background-color:yellow;
Hello, my title is {{!!title}}
@@

This makes tiddler A display its title with a yellow background (see Styles and Classes in WikiText to learn about CSS style). Imagine that you want to display the title in the same way in tiddler B. But you don't want to copy/paste the style instructions, because you might want to change the background colour later and you want to keep it consistent among tiddlers. This looks like a typical case of transclusion, so let's try to transclude tiddler A in tiddler B the usual way with {{A}}. You should see the following content in tiddler B:

Hello, my title is A

The style is applied as expected, but the title is wrong: we want {{!!title}} to refer to the target tiddler B, and not the source tiddler A.

The solution is to use a template. In this case, the source tiddler A is called the TemplateTiddler, and it is applied to tiddler B using the notation {{||A}}. The difference is that any TextReference which does not refer explicitly to a specific tiddler is applied to the current tiddler, that is, the target tiddler. As a result, tiddler B now looks as expected:

Hello, my title is B

Usage

Transcluding via a template is like applying a mask: assuming that the source tiddler contains generic references (like eye holes in a mask), these will be replaced with the target tiddlers values (like the eyes of the person who wears the mask).

A template can be applied to any tiddler, not necessarily the current one. This is achieved using the full notation {{<target>||<template>}}. The default <target> is the current tiddler (this is what we used in the above example).

Examples

A predefined template to render tags nicely

You can apply the system template $:/core/ui/TagTemplate to a tag in order to see it as a tag pill with a drop-down menu:

{{Transclusion||$:/core/ui/TagTemplate}}

is rendered as Transclusion

See also: