Help:Templates/yo

If you have standard texts you want to include on several pages, the MediaWiki template feature comes into play. Unlike extensions and media files, there is no central repository for templates. Templates can be newly written or to save duplicating work already done, exported from another wiki e.g. Wikipedia, and then imported into the target wiki.

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 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 this template link is used, it will be replaced once and for all with the content of Template:Name as of the time the page with the link is saved: a copy of the contents of Template:Name will be substituted for the template link. The contents are then a part of the including page, and can be edited normally, separately from the original. Note: later changes to the source template page will not be propagated to the page with the template link.
 * — this was introduced to allow for substitution that doesn't break transclusion, see w: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 be 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, 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:

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 behavior. Reversing the order of the parameters, like so:

would produce this result:

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:


 * Examples:

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:

Named parameters are case-sensitive, so:

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 their arguments, in this way:

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

Since no arguments 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:

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

Often default values are used to specify alternate names of parameters. For example, if you have, the template will first look for a parameter named "a". If it is not set, it will use the parameter named "b". If neither "a" nor "b" is set, it will output nothing.

Evaluation
Generally speaking, template parameters are substituted into the template after tokenization, but as is. They are not evaluated until they are used.

This has a few consequences. First of all, if you have a  containing , and a   containing  , and put   on a page, mytemplate isn't transcluded, because tokens like "|" cannot be added by a template and keep their special meaning in templates. You can still use templates to control the name of a parameter or template, but you cannot split a template call amongst multiple templates.

The second consequence of this is dead-code elimination. If you make a template call like, and Template:Foo does not contain  , then the displaytitle is not used, since it is only evaluated when needed, and it there is no parameter to substitute it into, so it is never evaluated. This usually comes into play when using Extension:ParserFunctions, and can be especially noticed when used in combination with the  magic word that varies by user language.

Template calls starting with the magic word  or   are evaluated in a separate first pass that only happens at save time, along with ~ and links using the pipe trick. If they cannot be evaluated during the first pass, subst: calls are ignored, and safesubst: are treated as if a normal template.

Many but not all parser functions, parser tags and trancluded special pages are not directly included like templates but instead are replaced by a "strip marker". This means you cannot manipulate the results with parser functions like padleft: or similar functions from extensions, as they see the strip marker instead of the result of the parser function.

Recursion in templates
Including a template in itself won't throw MediaWiki into infinite recursion. MediaWiki will stop the recursion with the template's name in bold. For example, if the content of Template:Aaaa is, it'll display "a a Template loop detected:  Template:Aaaa z z".

Forbidden idiom
This safeguard precludes a potentially useful template idiom where a template self-normalizes its own calling arguments. In this forbidden example  can either be called   or. If called in the first manner, it recurses into itself with the second argument structure (obtained using string parser functions), which then follows a unified processing path.



If  is modified to recurse into   and   is an identical manual copy of   this idiom works fine as the self-recursion safeguard operates dynamically and not statically.

A feasible way for the MediaWiki software to loosen the self-recursion rule would be to require that each recursive call have a distinct argument count from all previous active calls, at most once recursing with the argument count non-decreasing. That would provide a strong guarantee against infinite self-recursion while enabling useful idioms such as the one described here in a flexible manner.

If the processing path is of low complexity, a simple solution using only one template is to handle each calling convention on a separate if/else branch, duplicating the logic of the processing path within each case. If the processing path is more complex, each call-structure case can delegate to an implementation template with a unified call structure which provides the final template behaviour.

Tables in parameters
Since the syntax for wikitables involves pipes in single braces ({ }) and using the pipe trick will not work in transclusion parameters, one will have to create a table as a separate page and transclude it from there.

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 . To force the re-categorization of a particular page, open that page for editing and save it without changes.
 * 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  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. The focus is on what is inside these two tags.

Everything outside tags is discarded in the transclusion. Even sections tagged includeonly are discarded in the transclusion unless they are also tagged as onlyinclude. The focus is on what is outside this tag.

Nesting of these tags is also possible.

The three partial transclusion tags enable all possible combinations of what is processed and rendered. Comments also fill a role.

Organizing templates
For templates to be effective, users need to find them, and find out how to use them.

To find them, users can:
 * 1) Click ' > '
 * 2) In the ' list, choose Template and click '.

To give usage information, include an example like this one on the template page:

Usage
Welcome users:

Then, an editor can simply copy and paste the example to use the template.

Linking to a template
A template page can be linked to like any other wiki page. For example, the link Template:Navbar is generated using the wikicode.

On many wikis, Template:Tl can be used to provide a link to a template formatted in a way that shows the "double curly-braces" wikicode necessary to transclude the template without actually doing the tranclusion. For example, the code  may be used to create the link Navbar.

This construct is commonly used when referring to templates in template documentation, on help pages, and on talk pages. The same effect can be achieved by using, but the tl approach involves much less typing. On any given wiki the Tl template, if it exists, may or may not render the text in a "code" element or as monospace type. If not (as on this wiki), another similarly named template may do so. See, for example, the "See also" section of our Template:Tl documentation.

Copying from one wiki to another
Templates often require CSS or other templates, so users frequently have trouble copying templates from one wiki to another. The steps below should work for most templates.

MediaWiki code
If you have import rights (specifically importupload) on the new wiki:


 * 1) Go to Special:Export on the original wiki, and download an .xml file with the complete history of all necessary templates, as follows:
 * 1) * Enter the name of the template in the big text box, e.g. "Template:Welcome". Pay special attention to capitalization and special characters — if the template name isn't exactly correct, the export may still occur but the .xml file will not have the expected data.
 * 1) * Select the box "".
 * 1) * Select the box "".
 * 1) * Click "".
 * 1) Go to Special:Import on the new wiki and upload the .xml file.

If you don't have import rights on the new wiki:


 * 1) Go to the template you want to copy from the original wiki. Go to the edit page, and copy all the wikitext
 * 2) On the new wiki, go to the page with the same name as the template you copied. Hit create/edit and paste the wikitext you copied. In the edit summary of each template, link to the original page for attribution.
 * 3) Back in the original wiki at the edit window, below the edit box, look at the list of "Templates used on this page". For each template listed follow these instructions. Also do that for any template used by any of these templates, and so on.

This will copy the entire code necessary, and will suffice for some templates. Note that only page elements parsed in rendering the page get exported, so, for example, documentation subpages are not exported as part of this process. If it doesn't work also check for red links listed under "Pages transcluded onto the current version of this page:", below the edit box. If there are any repeat the above steps for these as well and also copy the code in the modules.

After successfully importing the template and all its linked templates from the other wiki, edit it to change customisations to suit your wiki. For example to change a logo, remove redundant categories or red links.

Extensions
An extension often used in templates is ParserFunctions. Visit page and check if any of the functions listed there are used in the templates you've copied. If so, you have to install the extension. To install it, you'll need system admin access to the server of your MediaWiki installation.

Another dependency that may be used in templates, especially those on Wikipedia, is Lua. Having   in template code is a good sign for it. In case it's used, you need to install the extension and system admin access is required too. See that page for more instructions about installing and using the extension.

CSS and JavaScript code
Besides MediaWiki code, many templates make use of CSS and some rely on JavaScript to work fully. If the copied templates are not behaving as expected, this may be the cause. To copy the required CSS and JavaScript to your wiki you'll normally need to have admin privileges, because you'll be editing system messages in the "MediaWiki:" namespace.


 * 1) Look for the use of CSS classes (text like  ) in the template text. If those classes appear in "MediaWiki:Common.css" or "MediaWiki:Monobook.css" on the original wiki, copy those classes to "MediaWiki:Common.css" on the new wiki and check if the template is now fine.
 * 1) If the copied template is still not working as expected, check if there is code in "MediaWiki:Common.js" or "MediaWiki:Monobook.js" on the original wiki. If so, you can try copying it to "MediaWiki:Common.js" on the new wiki. Normally, it is a good idea to only copy code from trusted sources, and first browsing the code to identify and select the parts that are relevant. You may find comments that can serve as clues to identify the functionality of each part.