My first major programming projects, before university, involved coding using wiki templates.

Wiki templates are snippets designed to be used on other pages. For example, the earliest version of Template:Stub had the content

''This article is a [[Wikipedia:The perfect stub article|stub]]. You can help Wikipedia by [[Wikipedia:Find or fix a stub|fixing it]].''

It could be included in an article as {{stub}}. If the text wanted to be changed (or to have a box set around it), it would only need to be changed in this one place.

Templates commonly take parameters: either numeric or keyworded, which when passed in change the text content. For example, a template that eases linking to other templates, Template:tl


Called using {{tl}} displays {{tl}}.

The initial {{ characters need to be escaped, as you can call one template from another template.

{{LastMonth}} <- {{Month}} -> {{NextMonth}}

and additionally you can pass in a parameter with the name of the template to call:

The output of Template:{{{1}}} is {{{{{1}}}}}.

Using this, you can create data pages for items:

name=helmet turtle|
plural=helmet turtles|

When a template page is displayed, the text inside <includeonly> is not included. When a template is included in a page (i.e. as {{template}}), the text inside <noinclude> is not included. This template says to call the template provided as the format variable (above, item/meta) with the parameters name=helmet turtle, plural=helmet turtles, image=turtle.gif, and one extra numeric parameter, defaulting to empty (not provided above, but you could enter it as {{Data:Helmet turtle|format=my_template|my_extra_variable}}).

The above style is good if you need all of the variables (or more than one), as there’s a limit on how many templates can be transcluded in a single page that you might breach if you took them all individually. To extract a single one, you can use #switch:


This lets you call pass in a keyword (e.g. image) as the second parameter, and get either the value of that parameter or the third parameter you’ve provided as a default (using the spare numeric parameter on the data page above).

Note the interesting behaviour here – {{{format}}} is replaced with #switch: mykey, and then the whole construct is interpreted as a {{#switch}} parser function. This delayed parsing lets you make templates that can embody very complex behaviour.