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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.

Hello! Welcome to the wiki.

{{Welcome}}

Hi there! Welcome to this wonderful wiki.

Because the template call remains in the pages's source, any subsequent change to Template:Name will be seen on the page containing the template call. Also, the page will be listed among those that "link to" the template.

That is, a copy of the contents of Template:Name will be substituted for the template call. No link is maintained between the page and the template, so each can be edited further without affecting the other. In effect, there is little difference between substituting the content in this way and simply typing it into the page's source "manually". See Help:Substitution for more information.

See Help:Substitution for more information.

For example, {{msgnw:Template:Thankyou}} displays:

<noinclude> <languages/> </noinclude> '''A little thank you...''' for {{{reason|{{{1}}}}}}. hugs, {{{signature|{{{2}}}}}} <noinclude> [[Category:Template examples{{#translation:}}|{{PAGENAME}}]] </noinclude>

Regardless of what syntax is used, the name of the template can be relative to the current page For example, if {{/bar}} is called on page foo, it will transclude the page foo/bar.

It can also be generated dynamically. For example, {{ {{foo}} }} calls Template:foo and interprets the result as the name of another template to call.

So that the note will look similar everywhere it is used, you can define a template called Template:Thankyou , 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 {{{1}}}.
hugs, {{{2}}}

{{Thankyou|all your effort|Me}}

{{Thankyou|Me|all your effort}}

{{Thankyou|2=Me|1=your friendship}}

Examples:

{{Thankyou|1=adding “=”|2=Me}}

produces:

A little thank you... for adding “=”. hugs, Me

Warning:

This also requires numbering each other parameter.

'''A little thank you...'''
for {{{reason}}}.
hugs, {{{signature}}}

{{Thankyou|signature=Me|reason=being who you are}}

{{Thankyou|signature=Me|Reason=being who you are|reason=being case-sensitive}}

For example, {{Thankyou|supporting both parameter types|signature=Me}} results in:

A little thank you... for supporting both parameter types. hugs, Me

Be careful when doing this, because it can result in conterintuitive results as unnamed parameter counts are based only on the unnamed parameters, not the named parameters. For example, {{Thankyou|Me|reason=supporting both parameter types}} results in:

A little thank you... for supporting both parameter types. hugs, {{{2}}}

The template is coded to prefer the named parameter for the reason over the unnamed parameter, resulting in the "Me" being lost and no signature being given. This results in a default value of {{{2}}} being shown, as explained below.

{{Thankyou}}

A little thank you... for {{{1}}}. hugs, {{{2}}}

'''A little thank you...'''
for {{{reason|everything}}}.
hugs, {{{signature|Me}}}

Often default values are used to specify alternate names of parameters. For example, if you have {{{a|{{{b|}}} }}}, 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.

If raw parameter syntax is generated by the above template call, and then passed through to another template, it is not interpreted as a parameter. This means that {{Thankyou2 }}, which just calls {{Thankyou }} with no parameters, does not work: {{thankyou2|everything|me}} -> A little thank you... for {{{1}}}. hugs, {{{2}}} .

You instead need to explicitly pass the parameter to the other template, i.e if {{Thankyou3 }} contains

{{thankyou|{{{1}}}|{{{2}}}}}}

then {{thankyou3|everything|me}} -> A little thank you... for everything. hugs, me } works properly.

This example does not preserve emptiness vs. undefinedness in parameter values - you would need more complicated syntax if you wanted to do that.

The {{t2demo|| a }} (refer to {{T2demo }} ), with a double pipe, sets the first parameter to an empty string instead of leaving it undefined. It produces the output start--middle- a -end, similar to how {{t2demo|1=|2= a }} results in start--middle- a -end. On the other hand, explicitly setting the parameter "2" to "a," results in the first unnamed parameter being left undefined:

• Use {{{p|}}} exclusively instead of {{{p}}} or q where "q" is a non-empty value.
• Use conditional checks like {{#if:{{{p|}}}|..{{{p}}}..|..}}, to ensure {{{p}}} is only used when it has a value.

If for some reason you want to treat undefined parameters differently from empty parameters or any other possible value you can compare the same parameter twice with different defaults, i.e {{#ifeq:{{{foo|bar}}}|{{{foo|baz}}}|parameter is defined|parameter is undefined}}.

Unnamed parameters can include equals signs, but this must be done indirectly. Here are some methods using template:T1demo:

Default Value for Undefined Parameter

Assign a default value to an undefined parameter:

{{T1demo|{{{1| a=b }}}}}

This renders as: start a=b end.

Using the {{=}} parser function

Use a parser function that safely includes an equals sign:

{{T1demo| a{{=}}b }}

This renders as: start a=b end.

HTML Entities

Replace the equals sign with an HTML entity for display:

{{T1demo| a=b }}

This renders as: start a=b end.

• Rendering curly brackets have two options:
  • Use <nowiki>{{</nowiki> or { for {
  • Use <nowiki>}}</nowiki> or } for }.
• Use [ for [ and ] for ].

Unmatched curly brackets

{{T1demo| <nowiki>{{</nowiki>content<nowiki>}}</nowiki> }}

This correctly renders the braces without breaking the template.

Unmatched square brackets

{{T1demo| text [link] more text }}

This correctly renders the braces without breaking the template.

This renders as: start text [link] more text end

{{T1demo|abc]]def[[ghi}}

{{T1demo|abc<nowiki>]]</nowiki>def<nowiki>[[</nowiki>ghi}}

This renders as: startabc]]def[[ghiend

An alternate technique for passing arguments with unmatched brackets is to wrap them in another template. In that situation, (which exists with {{(( }} and {{)) }}) on this wiki), the unmatched brackets will be rendered literally, and not decoded as another template call. For example:

{{t1demo|{{((}}t1demo{{))}}}}

results in: start{{t1demo}}end

When substituting a template, template inclusions are parsed once when the subst happens (with the same caveats explained above) and then a second time when rendering the resulting wikitext. For example:

{{subst:((}}t1demo|foo}}

will expand on save to:

{{((}}t1demo|foo}}

which will then render as:

startfooend

If the wikitext generated via the first subst itself includes "subst:" syntax it will not be processed on the same save, but may be on the next save. This technique may be used to implement recursive substitutions that take multiple saves to evaluate.

A parameter value cannot contain a pipe character (|), because it would be interpreted as the end of that parameter and the start of the next parameter. This can be worked around by using the parser function {{!}}, or the HTML entity &124;. The two methods of doing this have slightly different behavior, which can be relevant in some corner cases like when a template is producing wikitable syntax.

Example: {{T1demo|abc|def}} produces: startabcend

The "def" doesn't display because it is treated as part of another unnamed parameter, which the template does not use.

{{T1demo|abc{{!}}def}} produces: startabc|defend

The "def" displays properly.

{{T1demo|abc|def}} produces: startabc|defend

The "def" displays properly again.

Since templates ignore parameters they are passed but do not handle specifically, they can be used as a way of a adding extra whitespace or unused content to the template call.

For example:

{{template name|foo|bar|baz|mumble|quux}}

is equivalent to, assuming the template doesn't recognize SPACEN as a parameter name:

{{template name|SPACE1=
|foo|SPACE2=
|bar|SPACE3=Random stuff
|baz|SPACE4=
   |mumble|SPACE5=
  quux
}}

It is also possible to use the same name for each spacer (often the empty string), but this will populate Category:Pages using duplicate arguments in template calls, which many wikis prefer to keep empty to catch instances of user error.

This can be used to make the template render in a way similar to its output, like showing each row of w:Template:Chess position on its own like to make the wikitext also look like a chessboard.

It may be wise for a template to add a link or category to a page if a certain parameter or combination of parameters is used, to make if possible to easily determine what pages are using a given parameter, and thus what the impacts of changing that parameter in the template would be.

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:

1. If you have a Template:Start containing {{mytemplate, and a Template:End containing |foo=bar}}, and put {{start}}{{end}} 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.
2. Dead-code elimination: If you make a template call like {{foo|{{DISPLAYTITLE:Bar}} }}, and Template:Foo does not contain {{{1}}}, then the DISPLAYTITLE is not used, since it is only evaluated when needed, and 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 int: magic word that varies by user language. This isn't perfect, and in some cases even if the result of expanding a template is not used (because it is part of an if statement condition, for example), the process of evaluating it can still have side effects. For example, any links produced or other templates used will still be added to Special:WhatLinksHere even if they are not displayed.

Template parameters are pass by value, which means a template cannot modify its arguments. Parameters are treated as associative array, and parameter names are evaluated before parameter values. If the same parameter name is given more than once (either as named or unnamed), only the last instace is used, and the page is added to Category:Pages using duplicate arguments in template calls.

Template calls starting with the magic word subst: or safesubst: 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.

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 a {{Aaaa}} z, it'll display "a a Template loop detected: Template:Aaaa z z".

This safeguard precludes a potentially useful template idiom where a template self-normalizes its own calling arguments. In this forbidden example template:d can either be called {{d|20200311}} or {{d|y=2020|m=3|d=11}}. 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:{{{1|}}}|{{d|y={{#sub:{{{1}}}|0|4}}|m={{#sub:{{{1}}}|4|2}}|d={{#sub:{{{1}}}|6|2}}}}|<!-- processing path with arguments y,m,d regardless of original call pattern -->}}

If template:d is modified to recurse into template:d/2 and template:d/2 is an identical manual copy of template:d 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.

• the built-in magic word {{!}} provides an "escaped" version of | since MediaWiki 1.24
• the built-in magic word {{=}} provides an "escaped" version of = since MediaWiki 1.39

Before the introduction of these magic words, many wikis used templates to accomplish the same things. On such a wiki, the magic words take precendence over the same-named templates.

Table code:

{| class=wikitable
!A!!B!!C
|-
|A1||B1||C1
|-
|A2||B2||C1
|}

Escaped table code:

{{{!}} class{{=}}wikitable
!A!!B!!C
{{!}}-
{{!}}A1{{!}}{{!}}B1{{!}}{{!}}C1
{{!}}-
{{!}}A2{{!}}{{!}}B2{{!}}{{!}}C2
{{!}}}

Note that the first left-brace ({) is interpreted as a literal left-brace character because it is immediately followed by the {{!}} magic word. Similarly, the last right-brace (}) is interpreted as a literal right-brace character because it is immediately preceeded by the same magic word. However, in some cases these brace characters do cause problems, so some wikis provide templates for escaping these characters, as well:

• the template call {{(}} might provide an "escaped" version of {
• the template call {{)}} might provide an "escaped" version of }

Some wikis go even further and provide other convenience templates like {{(!}} ({|), {{!)}} (|}), {{!!}} (||). On such a wiki, the code can be simplified a bit to this form:

{{(!}} class{{=}}wikitable
!A!!B!!C
{{!}}-
{{!}}A1{{!!}}B1{{!!}}C1
{{!}}-
{{!}}A2{{!!}}B2{{!!}}C2
{{!)}}

The template's page when viewed directly appears exactly as the template would render without any parameters. If the template requires parameters to function properly, this will result in raw wikitext syntax or errors as a result of them being missing.

• If a parameter has no default value, it shows as the literal text {{{1}}}, indicating the template needs a parameter.
• If a parameter has an empty default value (it is written as {{{1|}}}), it displays nothing, which achieves the intended effect but lacks clarity for self-documentation. Using a non-empty default value like {{{1|$1}}} could clarify a parameter's role, especially for templates involving images.
• If a parameter without a default is passed to the #expr parser function, it results in an error message: "Expression error: unrecognized punctuation character '{'."
• If a template creates a table, it's helpful for the template page to show the table's structure rather than the wikitext used to make it. To do this, the table syntax isn't enclosed in tags, and each table element includes both ‎<noinclude>...‎</noinclude> and ‎<includeonly>...‎</includeonly> parts where needed.

It's a common pattern on some wikis to use a template like {{Documentation }} to transclude the documentation from a subpage of the template. For example, Template:Void is documented at Template:Void/doc.

Everything outside ‎<noinclude> and ‎<includeonly> 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 ‎<onlyinclude> 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 only on what is inside this tag.

For example, if a page like Help:Templates/onlyinclude demo has the wikitext:

abc<onlyinclude>def</onlyinclude>ghi<includeonly>jkl</includeonly>

The result of transcluding it is def.

The three partial transclusion tags enable all possible combinations of what is processed and rendered. Comments also fill a role. Inclusion tags are respected when using {{subst:templatename}}, but they are not respected when using {{msgnw:templatename}} as that displays the raw wikitext without any processing.

To transclude different sections of a template on different pages, you can wrap the content in onlyinclude tags and use an if statement on parameters to select which section.

Consider "Template:Example" with this wikitext:

== Section 1 ==
{{#ifeq:{{{1|1}}}|1|
Content of section one.
}}
{{#ifeq:{{{1|2}}}|2|
== Section 2 ==
Content of section two.
}}

This will render both sections on the example page itself, and allow other pages to transclude the first section with {{example|1}} and the second section with {{example|2}}.

Another approach is to use literal parameter syntax instead:

{{{section1|
== Section 1 ==
Content of section one.
}}}
{{{section2|
== Section 2 ==
Content of section two.
}}}

Transclude the first section with {{example|section2=}} and the second section with {{example|section1=}}. If neither parameter is used, then both sections will display.

A third approach is to use Labeled Section Transclusion.

<noinclude>
== Usage ==
Welcome users:
{{Thankyou|reason=your reason|signature=your signature}}
</noinclude>

While editing a page, a list of all templates used is available under the editing form, in a collapsible section titled "Maler som brukes på denne siden:" (also named "Maler brukt i denne forhåndsvisningen:", or "Maler brukt i denne seksjonen:" depending on the context). This list provides a convenient link to the template's page, as well as information about its protection status. Redirected templates are shown in italics, with the redirect target added as a separate list item.

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 {{[[Template:Navbar|Navbar]]}}, 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.

The name of a template is case-sensitive excluding the first character.

You make redirects for alternate capitalizations. For example, if a template is named "AdminAbbr", you can create a redirect named "Adminabbr". This way, the template can be called with either {{AdminAbbr}} or {{adminabbr}}. If an editor prefers a mix of upper and lower case for clarity, they can use functions like lc or uc. For instance, instead of {{CURRENTINTERNETTIME}}, they could use {{ {{uc:CurrentInternetTime}} }}

Because template names are interpreted in the same way to the names of other pages, underscores are replaced with spaces, and any text after a number sign (what would be a anchor in a standard link) is ignored.

An underscore _ can be alternative to a blank space.

Templates can be used for any situation in which one wants two or more pages to contain identical or similar content that is edited together rather than independently. They can be used to:

• Provide structured elements on many pages, like infoboxes, maintenance templates, navigational boxes, etc.
• Perform calculations used as a programming tool on various pages, like w:Template:Sum.
• Build composite pages that display the content of multiple existing pages together, like w:WP:Village pump (all) which includes content from each section of the village pump. The content of these pages can either be shown individually, or together, but the revision history, watchlist, etc. will only pick up changes to the transcluded pages and the raw wikitext of the composite page itself, not implicit changes to the composite page.
• Share some content between a few related pages. For example, the list at Help:Preferences#Beta features is duplicated at Beta Features#Current Beta Features. While on MediaWiki.org that is built using Extension:LabeledSectionTransclusion instead, it could have been done using a template.
• Store content referenced multiple times on the same page, so it only has to be written and calculated once. For example w:Template:Cite Monumentenregister/URL is called twice by w:Template:Cite Monumentenregister in two different places, and using another template means the URL pattern only has to be written once in the base template.
• Use templates as a programming element to generate a loop: if Template:A calls Template:B 10 times with different parameters, then that crudely simulates a for loop. If Template:B calls Template:C 10 times, then you have a nested loop of 100 calls of Template:C. But keep in mind that it is easy to run into the template limits when using templates as advanced programming constructs, and using Scribunto is generally clearer and easier to follow.

It is possible, if allowed by the wiki configuration to transclude templates from other wikis. This configuration setting is disabled on Wikimedia wikis. Otherwise, you need to manually copy the template and its dependencies from the source wiki to the destination wiki to use it.

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, consequently 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.

An extension often used in templates is ParserFunctions. Visit page Extension:ParserFunctions and check if any of the functions listed there are used in the templates you've copied. If so, you have to install the ParserFunctions 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 {{#invoke: }} in template code is a good sign for it. In case it's used, you need to install the Scribunto extension and system admin access is required too. See that page for more instructions about installing and using the extension.

If a page uses a redirect as a template, the redirect is resolved before processing the template and the target is used instead. This won't work if the target doesn't exist (a broken redirect), or is itself a redirect (a double redirect).

A page that just includes another page as a template might look like a redirect, but there are several differences between them:

• The header of the result displays the title of the page it came from.
• No "Redirected from" message is shown.
• Buttons like edit, watch, talk, history, "what links here," and "last modified" point to the referring page. To access the target page, use a section edit link and navigate from there.
• Unless includeonly and/or noinclude tags are used, the referring page shares the same categories as the target page.
• "Double redirects" work when one or both are this type of pseudo-redirect.

MediaWiki also supports parser functions, which function similarly to templates but follow slightly different syntax:

• Parser functions utilize a ":" instead of the initial "|".
• An edit page does not display parser functions used on that page.
• There is no "What links here" feature for parser functions to identify the pages where they are utilized.
• Parser functions templates do not generally accept named parameters, so equal signs generally have no special significance. For example:

{{ #if: not blank | x=abc }} gives x=abc

• Manual:Expr parser function syntax
• Help:Substitution
• w:Help:Template
• Manual:Advanced templates – describes even more advanced techniques such as dynamic template calls and variable parameter names
• Help:Multiple-instance templates - on the use of multiple instances of the same template on a page.
• Manual:Newlines and spaces#Automatic newline

• Help:Magiske ord – fancy stuff you may find in some templates
• Help:Extension:ParserFunctions – additional fancy control functions such as #if and #switch
• Help:Parser functions in templates – guidance on using parser functions in templates
• Help:TemplateData
• Help:Extension:ParserFunctions
• Extension:Scribunto

• Help:ExpandTemplates
• Help:Eksterne søk – a template special use case example
• Manual:Importing Wikipedia infoboxes tutorial
• Extension:PageTemplates
• Manual:Opprett sider med forhåndslastet tekst – Using templates as the starting text of a page
• Help:Transclusion – embedding pages from namespaces other than Template:
• Manual:Template limits
• Help:What links here
• Special:Mostlinkedtemplates - shows the templates with the most uses
• Special:Unusedtemplates - shows templates with no uses (although they may be substituted)
• Manual:$wgEnableScaryTranscluding - using templates from other wikis
• w:WP:Anatomy of a template
• w:Wikipedia:Transclusion costs and benefits
• Manual:Parser.php
• Help:Extension:TemplateSandbox - for previewing your changes to a template as it renders elsewhere

• Miraheze template repository - MediaWiki templates intended for general use.