Help:Templates

If you have standard texts you want to include on several pages, the MediaWiki template feature comes into play.

Creation
Templates are standard wiki pages whose content is designed to be transcluded (embedded) inside other pages. Templates follow a convention that the name is prefixed with, assigning it to that namespace; besides this, you can create them like any other wiki page.

The simplest use of templates is as follows. If you create a page called "Template:Welcome" with contents:

Hello! Welcome to the wiki.

you'll have created your first template! If you then insert the code:

in any other page, when that page is viewed the text "Hello! Welcome to the wiki." will appear instead of. The template content is "transcluded" into the other page, i.e. it is integrated in the page.

You can then insert  at any point of any page where you wish to welcome someone. Suppose it is used in 100 pages. If you then change the template contents to:

Hi there! Welcome to this wonderful wiki.

and revisit any of the 100 pages where the template was used, you'll see the new text instead of the original one. In this way, you have changed the content of 100 pages without editing them, because the template is transcluded into these pages.

This is the basic mechanism. There are several additional features of transclusion that enrich this mechanism and make templates very useful.

Usage
Templates can be used in other pages in these ways:
 * — as described above, this link will be dynamically replaced by the current content of Template:Name at the time the page with the template link is loaded. The link will remain unchanged in the page's source.
 * — when used, this template link will be substituted with a copy of the contents of Template:Name in the source of the transcluding page, as of the time the page with the link is saved; the contents are then a part of the including page, and can be edited normally, separately from the original. Note: changes to the source template page will not be propagated to the page with the template link.
 * — this allows for substitution that doesn't break transclusion, see wikipedia:en:Help:Substitution.
 * includes the template in a form that displays it as raw wiki syntax (the way  does) when the page containing it is fetched.

In fact, an ordinary wiki page can also be used as a template, simply by specifying the namespace it resides in, so:
 * includes
 * includes
 * includes
 * replaces itself with the contents of

If no such namespace exists, the full title is assumed to be a template:
 * includes

Parameters
To enrich the mechanism of transclusion, MediaWiki allows parameters to be passed to a template when it is transcluded. Parameters allow the template to produce different contents or have different behaviors.

Suppose you wish to insert a little thank you note in the talk page of other users, such as:

The thank you note will have a reason (in this case, "all your effort") and a signature ("Me"). Your objective is that any user is able to thank any other user, for any reason whatsoever.

So that the note will look similar everywhere it is used, you can define a template called Template:Wikihelp example, for example. Although the note should look similar whenever a user thanks another user, its specific contents (i.e. the reason and the signature) will be different. For that reason, you should pass them as parameters. If we ignore the remaining elements to format the box and place the image, the core content of the template will be this:

A little thank you... for. hugs,

Notice the use of  and. This is the way to identify, within templates, the parameters that will be passed in when the template is used. Note that, within the template, each parameter is surrounded by three braces. This is different from normal template name usage.

When using the template on a page, you fill in the parameter values, separated by a "pipe" character. MediaWiki allows parameters to be passed to the template in three ways: Anonymously, Numbered, and Named.

Anonymous parameters
To pass in anonymous parameters, list the values of those parameters sequentially:

In this case, the  template receives parameters   and , producing:

The order in which anonymous parameters are passed in is crucial to its behaviour. Reversing the order of the parameters, like so:

would produce this result:


 * Note: identifying parameters by order (with  ,   etc.) works only with anonymous parameters. If your page identifies any parameter by number or name, as shown below, this method will no longer be available to the template which receives them.

Numbered parameters
To pass in parameters by number, identify each parameter when passing it:

This time, template  receives parameters   and , though they have been supplied in inverse order, and produces:

Named parameters
The third way of passing parameters is by name, instead of numbers. In this case, the template contents would be changed to:

A little thank you... for. hugs,

Within the template, we use  and   to identify each parameter, instead of a number. To pass these parameters by name, identify each parameter when passing it:

In this case, template  receives parameters   and   and produces:

The advantage of using named parameters in your template, besides also being flexible in the order parameters can be passed, is that it makes the template code much easier to understand if there are many parameters.

Default values
If you transclude a template that expects parameters, but do not provide them, in this way:

in the numbered parameters example above you would get the following:

Since no parameters were passed in, the template presents the parameters themselves, instead of their respective values. In these cases, it may be useful to define default values for the parameters, i.e. values that will be used if no value is passed in. For example, if the template contents are changed to:

A little thank you... for. hugs,

then  defines that if no parameter   is provided, then the value   will be used. Similarly,, defaults parameter   to value. Now, transcluding the template again without passing any parameter, results in the following:

Control template inclusion
By default, a template's content is displayed in its entirety, both when viewed directly and when included in another page. However, you can control which parts of a template will be seen and included by the use of the  and tags.

Anything between  and   will be seen only when the template's page is being viewed directly, but not when it is included in another page. This is useful when you want to include text or code in a template that you do not want to propagate to any pages which include it, such as:
 * Category links when categorizing the template itself
 * interlanguage links to similar templates in other languages
 * Explanatory text about how to use the template

Likewise, anything between  and   will be processed and displayed only when the page is being included, but not when the template page is being viewed directly, and is useful in situations such as:
 * Categorizing pages which include the template. Note: when changing the categories applied by a template in this fashion, the categorization of the pages which include that template may not be updated until some time later: this is handled by the job queue. To force the re-categorization of a particular page, open that page for editing and save it without changes. (see m:Help:Dummy edit)
 * Ensuring that the template's code is not executed when viewing the template page itself. Typically this is because it expects parameters, and its execution without parameters has an undesired result.

Everything outside  and tags is processed and displayed normally; that is, both when the template page is being viewed directly and when the template is included in another page.