Editing Help:Transclusion

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{{Broader|Transclusion}}
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'''Transclusion''' refers to the inclusion of the content from one document within another document by [[Reference (computer science)|reference]]. In Wikipedia, transclusion means the [[MediaWiki]] software retrieving the content from a ''source'' ''page'', often a ''[[Wikipedia:Template|template]]'', and incorporating it into the content of a ''target page''.

<!--How transclusion works-->
Similar to creating a [[Wikipedia:Link|wikilink]] using double square brackets (<code><syntaxhighlight lang="wikitext" inline="">[[Pagename]]</syntaxhighlight></code>), a page can be transcluded as a template by enclosing its title in double curly braces or double curly brackets: <syntaxhighlight lang="wikitext" inline="">{{Namespace:Pagename}}</syntaxhighlight>. Any changes made to the source page, or template, are automatically reflected on all pages that include the transcluded content.{{refn|group=lower-alpha|A [[Wikipedia:Purge|purge]] may occasionally be necessary to refresh target pages, ensuring they retrieve and display the latest content from the template or source page. This forces the MediaWiki software to clear the cached version of the page and reload it with the most up-to-date transcluded content.}}

<!--Namespace rules-->
If no [[Wikipedia:Namespace|namespace]] is specified, it is assumed to be in the [[Wikipedia:Template namespace|Template namespace]]. To refer to a page in the [[Wikipedia:MAINSPACE|Main article namespace]], it is necessary to prefix it with a colon (<code>:</code>). For example:
* <syntaxhighlight lang="wikitext" inline="">{{Pagename}}</syntaxhighlight> is the same as <syntaxhighlight lang="wikitext" inline="">{{Template:Pagename}}</syntaxhighlight>
* <syntaxhighlight lang="wikitext" inline="">{{Stochastic processes}}</syntaxhighlight> will transclude from the page [[Template:Stochastic processes]]
* <syntaxhighlight lang="wikitext" inline="">{{:Stochastic process}}</syntaxhighlight> will transclude from the page [[Stochastic process]] (an article, in the Main namespace)
* <syntaxhighlight lang="wikitext" inline="">{{Wikipedia:Assume good faith}}</syntaxhighlight> will transclude from the page [[Wikipedia:Assume good faith]]

<!--Controlling transclusion-->
Transclusion and what content it includes or excludes can be modified by using the invisible [[Wikipedia:Wikitext|wikitext]] tags {{tag|noinclude|open}}, {{tag|onlyinclude|open}}, {{tag|includeonly|open}}, and {{tag|section|open}} on the {{em|source page}}, as further outlined in {{Section link|Help:Transclusion|Transclusion markup|nopage=y}}.{{refn|group=lower-alpha|Transclusion relies on functions that parse the source page, meaning that the appropriate wikitext markup must be present on the ''source page'' for it to correctly include or exclude content. The specific tags used for this purpose determine how the content will be transcluded into the target page. Properly implementing these tags allows editors to control the visibility of certain parts of the content based on the needs of the target page.}} The first three tags enable {{Section link|Help:Transclusion|Partial transclusion|nopage=y}}, as opposed to the default behavior of double curly braces, which will transclude the entire source page's content. For {{Section link|Help:Transclusion|Selective transclusion|nopage=y}}, the {{tag|includeonly|open}} or {{tag|section|open}} tags can be used and sections of the source page named, then using [[Wikipedia:Parser functions|parser functions]] the template can be called with the section name as a [[Help:Template#Parameters|parameter]]: <syntaxhighlight lang="wikitext" inline="">{{#section:Pagename|Sectionname}}</syntaxhighlight>.

<!--Transclusion vs. Substitution-->
Transclusion events occur each time the ''target page'' is loaded and the template is rendered. A related event is [[Wikipedia:Substitution|Substitution]], where a template call is replaced with its transcluded source content at the time it is invoked in a ''one-time'' inclusion of the content. Unlike transclusion, which continuously updates the target page with changes from the source, substitution results in a ''one-time'' inclusion of the content, meaning that subsequent updates to the source content ''will not'' be reflected in the target page. For example, a template call for <syntaxhighlight lang="wikitext" inline="">{{Pagename}}</syntaxhighlight> with the <syntaxhighlight lang="wikitext" inline="">subst:</syntaxhighlight> prefix results in the substitution template call <syntaxhighlight lang="wikitext" inline="">{{subst:Pagename}}</syntaxhighlight>. When invoked, this template is replaced, also referred to as substituted, with the actual wikitext of the source page at the time of the call, thereby making it a permanent part of the target page.{{refn|group=lower-alpha|In simpler terms, the page is ''published'' or ''saved'', and any future changes to the source page will not affect this substituted content.}}

<!--Transcluding from Wikidata-->
It is possible to [[Wikipedia:Wikidata#Inserting Wikidata values into Wikipedia articles|transclude content from Wikidata]] into Wikipedia articles or other wikis.

==How transclusion works==
{{Transcluded section|Help:Transclusion/How Transclusion Works}}
{{/How Transclusion Works}}

==Transclusion syntax==

The general [[Syntax (programming languages)|syntax]] for transclusion on Wikipedia follows the format <syntaxhighlight lang="wikitext" inline="">{{Namespace:Pagename}}</syntaxhighlight>, where <code>[[Wikipedia:Namespace|Namespace]]:[[Wikipedia:Page name|Pagename]]</code> specifies the [[Wikipedia:Title|title]] of a Wikipedia page.

Similar to creating a [[Wikipedia:Link|wikilink]] using double square brackets (<code><syntaxhighlight lang="wikitext" inline="">[[Pagename]]</syntaxhighlight></code>), a page can be transcluded as a template by enclosing its title in double curly braces: <syntaxhighlight lang="wikitext" inline="">{{Namespace:Pagename}}</syntaxhighlight>. Any changes made to the source page, or template, are automatically reflected on all pages that include the transcluded content.{{refn|group=lower-alpha|A [[Wikipedia:Purge|purge]] may occasionally be necessary to refresh target pages, ensuring they retrieve and display the latest content from the template or source page. This forces the MediaWiki software to clear the cached version of the page and reload it with the most up-to-date transcluded content.}}

Wikipedia is structured using [[Wikipedia:Namespace|namespaces]], which organize pages based on their function. For example, a page titled {{Xtn|[[Wikipedia:Tips]]}} belongs to the Wikipedia namespace, with <code>Wikipedia:</code> as its namespace and <code>Tips</code> as its pagename. However, articles in the [[Wikipedia:Mainspace|Main namespace]], such as {{Xtn|[[Potato]]}}, do not require a namespace prefix when linked using <code><syntaxhighlight lang="wikitext" inline="">[[Potato]]</syntaxhighlight></code>, as Wikipedia assumes any wikilink without a specified namespace belongs to the Article namespace.

When transcluding pages, if no namespace is specified, Wikipedia defaults to the [[Wikipedia:Template namespace|Template namespace]]. To reference a page in the Article namespace within transclusion syntax, it ''must'' be explicitly prefixed with a colon {{Char|:}} (e.g., <syntaxhighlight lang="wikitext" inline="">{{:Potato}}</syntaxhighlight>).

=== Examples ===
{| class="table" style="padding:0.25em; margin-bottom:0.5em; border: 1px #dadde3 solid; background-color: #F5FAFF;"
| style="vertical-align:top;" | {{nowrap|[[File:Dialog-information.svg|20px|alt=blue lightbulb]] '''Outline''':}} || using <syntaxhighlight lang="wikitext" inline>{{Pagename}}</syntaxhighlight> or <syntaxhighlight lang="wikitext" inline>{{Template:Pagename}}</syntaxhighlight> will transclude the content of {{Xtn|{{fake link|Template:Pagename}}}}. Using <syntaxhighlight lang="wikitext" inline>{{:Pagename}}</syntaxhighlight> instead will transclude the mainspace article titled {{Xtn|{{fake link|Pagename}}}}. Including <syntaxhighlight lang="wikitext" inline>{{Namespace:Pagename}}</syntaxhighlight> transcludes a page in the defined namespace, such as {{Xtn|{{fake link|Help:Pagename}}}}.
|}

* '''Specifying namespace''': <syntaxhighlight lang="wikitext" inline>{{Namespace:Pagename}}</syntaxhighlight> will transclude the page titled <syntaxhighlight lang="wikitext" inline>Namespace:Pagename</syntaxhighlight>. For example, if a page has the wikitext <syntaxhighlight lang="wikitext" inline>{{Wikipedia:Notability}}</syntaxhighlight> in it, it will transclude the page {{Xtn|[[Wikipedia:Notability]]}} into it. Please note that <syntaxhighlight lang="wikitext" inline>{{WP:Notability}}</syntaxhighlight> would do exactly the same thing, as <code>WP:</code> is a [[Wikipedia:Namespace#Aliases|namespace alias]], which is [[Wikipedia:Shortcut#Namespace_aliases|automatically translated]] by the Wikipedia servers to <code>Wikipedia:</code>.

* '''Calling from the Article namespace''': If the namespace is omitted, but the colon is included, like <syntaxhighlight lang="wikitext" inline>{{:Pagename}}</syntaxhighlight>, the mainspace article <code>Pagename</code> will be transcluded. For example, <syntaxhighlight lang="wikitext" inline>{{:Notability}}</syntaxhighlight> will transclude the article [[Notability|{{Xtn|[[Notability]]}}]].

* '''Template namespace''': If both namespace and colon are omitted, like <syntaxhighlight lang="wikitext" inline>{{Pagename}}</syntaxhighlight>, the <code>Template:Pagename</code> will be transcluded. For example <syntaxhighlight lang="wikitext" inline>{{Notability}}</syntaxhighlight>, and also <syntaxhighlight lang="wikitext" inline>{{Template:Notability}}</syntaxhighlight>, will both transclude the [[Template:Notability|{{Xtn|[[Template:Notability]]}}]].

Additionally, specific {{Section link|Help:Transclusion|Template parameters|nopage=y}} and {{Section link|Help:Transclusion|Transclusion modifiers|nopage=y}} allow [[Parameter (computer programming)|parameters]] to be passed to templates, alter how transclusion occurs, and therefore the output customized. This is explained in more detail below.

=== Subpages ===

[[Wikipedia:Subpages|Subpages]], identifiable by a <code>/</code> prefixed in their page names, are pages related to a 'parent' page (e.g., <code>Namespace:Pagename/Subpagename</code> is a subpage of <code>Namespace:Pagename</code>). This feature is disabled in the Main, File, and MediaWiki namespaces, but not on their corresponding talk namespaces.

To transclude subpages:

* In general, use <syntaxhighlight lang="wikitext" inline>{{Namespace:Pagename/Subpagename}}</syntaxhighlight>. With exception:
** On the parent page of a subpage, the more specific general syntax mentioned above can be used or simply <syntaxhighlight lang="wikitext" inline>{{/Subpagename}}</syntaxhighlight>. 
** For a template namespace page, it is either the general syntax or <syntaxhighlight lang="wikitext" inline>{{Pagename/Subpagename}}</syntaxhighlight>.
** Article subpages are disabled on this wiki, but would otherwise be <syntaxhighlight lang="wikitext" inline>{{:Pagename/Subpagename}}</syntaxhighlight>.
* Alternatively, you can also use {{Section link|Help:Transclusion|Template parameters|nopage=y}} and {{Section link|Help:Transclusion|Transclusion modifiers|nopage=y}}.

For example, to transclude {{Xtn|[[Template:Like/doc]]}}, you could use <syntaxhighlight lang="wikitext" inline>{{Template:Like/doc}}</syntaxhighlight> or <syntaxhighlight lang="wikitext" inline>{{Like/doc}}</syntaxhighlight>. Note that subpage names are case sensitive, and <syntaxhighlight lang="wikitext" inline>{{Like/Doc}}</syntaxhighlight> would lead to a different page.

===Template parameters<span class="anchor" id="Template transclusion"></span>===
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{{further|Help:Template#Parameters}}
{{for|a quick guide to templates|Help:A quick guide to templates}}

The most common use of transclusion on Wikipedia is for [[Help:Template|templates]]. Templates are specially designed pages intended to be included in other pages using either transclusion or [[Help:Substitution|substitution]]. The standard syntax for transcluding a template titled {{Xtn|Template:Pagename}} is <syntaxhighlight lang="wikitext" inline="">{{Pagename}}</syntaxhighlight>.

Additionally, many templates support [[Parameter|parameters]], which are variables that allow templates to function in different ways by passing specific values, also termed ''[[Parameter (computer programming)#Parameters and arguments|arguments]]''. Templates may have no parameters, use a fixed number of parameters, or support a variable number of parameters. The number of parameters a template can accept ranges from one to multiple, depending on its design.

The exact syntax for using parameters varies by template. However, for a hypothetical template titled {{Xtn|Template:Pagename}} that accepts three parameters, the general format would be:

<syntaxhighlight lang="wikitext" inline="">{{Pagename|parameter1|parameter2|parameter3}}</syntaxhighlight>

{{shortcut|WP:UNNAMED|WP:POSPARAM|WP:POSITIONAL}}
Where each parameter in a template can be substituted with either a <code>value</code> or a {{Para|parameter name|value}} format when used in practice. Notice that each parameter is separated by a [[vertical bar]] (<code>|</code>). Parameters that take the form <code>value</code> are called ''unnamed'' or ''positional parameters'', while those in the form {{Para|parameter name|value}} are known as ''named parameters''. With unnamed parameters, the first, second, and third parameters correspond to {{Para|1}}, {{Para|2}}, {{Para|3}}, respectively, etc., in [[Wikipedia:Template documentation|template documentation]]. Unnamed parameters must be provided in the correct order and are best placed before named parameters.{{Refn|Otherwise using <code>value</code> on its own will not work, and the unnamed parameters must be called using their 'names', such as {{para|1|value}}, if named parameters precede them.|group=lower-alpha}}

For example, using the {{Xtn|[[Template:Collapse top]]}} with two unnamed parameters and one named parameter:

: {{y}} <syntaxhighlight lang="wikitext" inline="">{{Collapse top|This is the title text|This is a custom warning line|left=true}}</syntaxhighlight>
: {{y}} <syntaxhighlight lang="wikitext" inline="">{{Collapse top|left=true|1=This is the title text|2=This is a custom warning line}}</syntaxhighlight>
: {{n}} <syntaxhighlight lang="wikitext" inline="" style="background-color:#ffdad3;">{{Collapse top|left=true|This is the title text|2=This is a custom warning line}}</syntaxhighlight>

In this case, <code>This is the title text</code> and <code>This is a custom warning line</code> are the values of unnamed parameters {{Para|1}} and {{Para|2}}, while <code>true</code> is the value assigned to the named parameter {{Para|left}}. The last example shows how unnamed parameters should not be used after named parameters without their 'name'. Although this example includes three parameters, {{Xtn|[[Template:Collapse top]]}} can accept a variable number of parameters.

For more details, see [[Help:Template]]. Additionally, [[Wikipedia:Template index]] provides a categorized list of templates, including those for mainspace and other namespaces, along with a search function. Template parameters also play a role in the {{section link|#Parametrization method}} of {{Section link|2=Selective transclusion|nopage=y}}, allowing for more dynamic content inclusion.

===Substitution===
{{Main|Help:Substitution}}
Transclusion events occur each time the target page is loaded and the template is rendered. A related event is Substitution, where a template call is replaced with its transcluded source content at the time it is invoked in a ''one-time'' inclusion of the content. Unlike transclusion, which continuously updates the target page with changes from the source, substitution results in a ''one-time'' inclusion of the content, meaning that subsequent updates to the source content ''will not'' be reflected in the target page. For example, a template call for <syntaxhighlight lang="wikitext" inline="">{{Pagename}}</syntaxhighlight> with the <syntaxhighlight lang="wikitext" inline="">subst:</syntaxhighlight> prefix results in the substitution template call <syntaxhighlight lang="wikitext" inline="">{{subst:Pagename}}</syntaxhighlight>. When invoked, this template is replaced, also referred to as substituted, with the actual wikitext of the source page at the time of the call, thereby making it a permanent part of the target page.{{refn|group=lower-alpha|In simpler terms, the page is ''published'' or ''saved'', and any future changes to the source page will not affect this substituted content.}} 

For example, when <syntaxhighlight lang="wikitext" inline="">{{subst:Like}}</syntaxhighlight> is inserted in a page and the changes published, it would substitute that wikitext with the actual wikitext from {{Xtn|[[Template:Like]]}}. In practice, subsequent updates to {{Xtn|[[Template:Like]]}} ''will not'' be reflected in the page it was substituted into.

===Magic words===
{{Main|Help:Magic words}}
Magic words are not examples of transclusion. But some have a near identical double curly bracket syntax and similar action to transclusion. For example, <syntaxhighlight lang="wikitext" inline="">{{FULLPAGENAME}}</syntaxhighlight> renders the full [[Wikipedia:Page name|page name]] of any Wikipedia page, for example it returns {{Mono|{{FULLPAGENAME}}}} on this page. Like templates, some magic words can also take parameters, which are separated using a colon (<code>:</code>); for example <syntaxhighlight lang="wikitext" inline="">{{TALKPAGENAME:Help:Transclusion}}</syntaxhighlight> returns {{Mono|{{TALKPAGENAME:Help:Transclusion}}}}. 

Templates do exist for some magic words, for example [[Template:FULLPAGENAME]]; but these just invoke the related magic word and pass parameters using the verticle bar (<code>|</code>) to the magic word in anycase; for example like <syntaxhighlight lang="wikitext" inline="">{{FULLPAGENAME|value}}</syntaxhighlight>. But magic words parameters are best passed directly by using a colon, which bypasses the unnecessary use of a template call too. For example, <syntaxhighlight lang="wikitext" inline="">{{FULLPAGENAME|value}}</syntaxhighlight> is synonymous with <syntaxhighlight lang="wikitext" inline="">{{FULLPAGENAME:value}}</syntaxhighlight>, where the latter is preferred.

===Transclusion modifiers===
{{See|mw:Help:Magic words#Localization int|mw:Help:Magic words#Transclusion modifiers}}
A ''transclusion modifier'' is a type of specialist magic word for altering transclusion in some manner. An example of which is the <code>subst:</code> modifier discussed above in {{Section link|2=Substitution|nopage=y}}. Another example is <syntaxhighlight lang="wikitext" inline="">{{:Notability}}</syntaxhighlight>, where the colon character (<code>:</code>) forces transclusion to the main namespace. There are additional transclusion modifiers such as <code>[[Wikipedia:SAFESUBST|safesubst:]]</code>, <code>[[mw:Help:Magic_words#Localization_int|int:]]</code>, <code>[[mw:Help:Magic_words#Transclusion_modifiers|msg:]]</code>, <code>[[mw:Help:Magic_words#Transclusion_modifiers|msgnw:]]</code>, and <code>[[mw:Help:Magic_words#Transclusion_modifiers|raw:]]</code>. For more details on their usage, see {{slink|mw:Help:Magic words#Transclusion modifiers}}. Also see the modified commands <code>#section:</code>, <code>#section-x:</code> and <code>#section-h:</code> used for labeled section transclusion, see [[Help:Labeled section transclusion]] and the section {{Section link|2=Using the labeled section method|nopage=y}}.

==Usage <span class="anchor" id="Applications of transclusion"></span><span class="anchor" id="Usage"></span>==
Transclusion is commonly used in [[Wikipedia:Templates|templates]], allowing content to be embedded dynamically across multiple pages. However, it is also applied in other contexts, particularly within project space, where it facilitates the management of structured content.

===Composite pages===
{{Hatnote|See also a 2005 Village Pump discussion on [[Wikipedia talk:Template namespace/Archive 1#transcluding prose|transcluding article prose as an unusual issue not covered by policy]].}}

''Composite pages'' are created by transcluding multiple component pages, either entirely or in part, into a central page. The wikitext of a composite page may include [[Help:HTML in wikitext|HTML tags]] to embed content, typically from standalone pages that are not part of the template namespace. The primary purpose of composite pages is to consolidate related content for easier access.

==== Examples ====
* [[Wikipedia:Village Pump]] – mostly consists of the transcluded page {{Xtn|[[Template:Village pump]]}}.
* [[Wikipedia:Articles for deletion/Log]] – for example, [[Wikipedia:Articles for deletion/Log/2005 May 31]] aggregates discussions from multiple individual deletion pages, such as [[Wikipedia:Articles for deletion/Sp3tt]]. On this particular day, 75 component pages were included.
* [[m:Meta:Translation_requests|Meta:Translation requests]] – pages such as [[m:Meta:Translation/Coordination/List/Meta]] and [[m:Meta:Translation/Coordination/List/Main]] are transcluded within [[m:Meta:Translation/Coordination]].

The use of composite pages allows users to view multiple related pages in one location rather than navigating through individual links.

==== Characteristics ====
Composite pages function independently from their component pages in several ways. While changes made to a component page are reflected on the composite page, the composite page maintains its own edit history, recent changes log, page-watch settings, and protection levels, separate from those of its transcluded content.

The talk page of a composite page is used specifically for discussions about the composite itself rather than for the individual component pages it includes. However, in some cases, a composite talk page may also transclude discussions from its component pages, allowing for a [[Wikipedia:Centralized discussion|centralized discussion]] space.

When editing, users can modify sections of a component page directly from the composite page, see {{Section link|Help:Section#Editing sections of included templates|}}. Once changes are saved, they are applied to the original component page, ensuring consistency across all instances where the content appears.

For projects that support [[Wikipedia:Interlanguage links|interlanguage links]], a composite page aggregates all interlanguage links from its component pages. This can sometimes lead to multiple links pointing to the same language or page, reflecting the structure of the transcluded content.

===Pages with a common section===
{{shortcut|WP:COMMONSECTION}}
When two pages need to discuss the same material in the same way, they can share a section. For example, a section of an existing page may be transcluded to other pages. This may also involve creating a third page and transcluding that page onto both pages. This third page may be a standalone page in its own right for another purpose, or a subpage of either of the other two – except in the mainspace, where [[Wikipedia:Subpages|subpages are not allowed]]. The third page may be placed in the same namespace as the other pages or in template namespace – again, except for use in mainspace, where templates should not be used to store [[Wikipedia:What is an article?|article text]], as this makes it more difficult to edit the content (see [[WP:TG]]). Common sections like this should be marked with an explanatory header, such as using the templates {{Tl|Transcluding article}} or {{Tl|Transcluded section}} to create [[Wikipedia:Hatnote|hatnotes]] above the transcluded content, and/or given a special layout, to inform the reader that this section of the page is in a different location, since transcluding shared article sections can easily confuse novice editors and readers alike if left unmarked. All templates can be found at [[:Category:Transclude page content templates]].

This can be very useful when two [[WP:DAB|disambiguation]] pages share content,{{Disputed inline|talk=Wikipedia talk:Manual of Style/Disambiguation pages#Transclusion|date=September 2017}} or a [[Wikipedia:List|list page]] and a disambiguation page share content (see third example below).

Examples:
*The [[Help:Editing sections of included templates]] article is included in [[Help:Section]] with the markup <syntaxhighlight lang="wikitext" inline>{{Help:Editing sections of included templates}}</syntaxhighlight>. By including a heading in the included article, a user clicking the "Edit" link on that heading in [[Help:Section]] is automatically directed to edit [[Help:Editing sections of included templates]].
*{{pim|Help|Alphabetic order}}
* [[Joseph Gordon-Levitt]] transcludes the introduction of [[HitRecord]] into a summary section of the same name, rather than maintaining two copies of the identical text.

===Repetition within a page===
On pages where there is a lot of repetitive information&nbsp;— various kinds of lists, usually&nbsp;— it is sometimes useful to make a template that contains the repeating text, and then call that template multiple times.  For example, [[Template:EH listed building row]] is used repeatedly to construct tables in many articles.

Simple repetition of the same text can be handled with repetition of a parameter in a single template: e.g., {{tl|3x}}, where <syntaxhighlight lang="wikitext" inline>{{3x| howdy!}}</syntaxhighlight> produces <code>{{3x| howdy!}}</code>.

For more information on repetition, see also [[m:Help:Recursive conversion of wikitext]]. 

For more information on the current template system, see [[Wikipedia:Template namespace]].
<!-- saving a nice programming tutorial on template language 'til someone merges it somehwere
Cpiral moved it to [[wp:template namespace#Sandbox_for_experiments]], 9/12/2012
-->

==Partial transclusion==
{{shortcut|WP:PARTRANS}}
By using {{tag|noinclude|o}}, {{tag|includeonly|o}} and {{tag|onlyinclude|o}} markup, it is possible to transclude ''part'' of a page, rather than all of it. Such partial transclusions can be achieved by transcluding from any pages, including subpages. It is often useful to exclude part of a page in a transclusion, an example being with template documentation. 

For an example of how this technique can be applied to simplify the creation of [[Wikipedia:Summary style|summary articles]], see how part of the [[History of pathology]] (see the diff [http://en.wikipedia.org/w/index.php?title=History_of_pathology&diff=prev&oldid=207668817 here]) was transcluded into [[Pathology]] (see the diff [http://en.wikipedia.org/w/index.php?title=Pathology&diff=prev&oldid=207669487 here]) using the <syntaxhighlight lang="wikitext" inline>{{:History of pathology}}</syntaxhighlight> markup. The Pathology article at that time (see [https://en.wikipedia.org/w/index.php?title=Pathology&oldid=207669487 here]) mainly consisted of transcluded [[Wikipedia:Manual of Style/Lead section|lead paragraphs]] and other sections from a number of articles. Since then, the Pathology article has been rewritten, and does not include all these transclusions.

Another example can be found in the transclusion of part of [[HitRecord]] (introductory paragraph only) into a same-named summary section in [[Joseph Gordon-Levitt#HitRecord|Joseph Gordon-Levitt]].
{{anchor|Transclusion markup}} <!--Temp anchor until renamed section is checked for link breakage via ''what links here''-->
===Markup===
{{also|Help:Template#Noinclude, includeonly, and onlyinclude|Help:Category#Categories and templates}}

In transclusion, a source page is transcluded into a destination page. But with partial transclusion, only part of that source page will be transcluded into a destination page. But in addition, what is transcluded to a destination page does not have to be visible on the source page.

''Page rendering'' of a source page can be defined as the rendering of that source page when it is saved, which will be the same as the [[WP:preview|preview]].  We can call this rendering '''''here'''''.

''Transclusion rendering'' of a source page can be defined as the rendering of a destination page that has a source page transcluded into it; but only that part of the destination page that was transcluded from the source page. The preview of the transclusion rendering will again be identical. We can call this rendering '''''there'''''.

There are three pairs of tags involved in cases where page rendering ''here'' should differ from transclusion rendering ''there''. As described earlier, these are {{tag|noinclude|o}}, {{tag|includeonly|o}} and {{tag|onlyinclude|o}}. These tags are invisible, but affect both page rendering ''here'' and transclusion rendering ''there''. These tags pair-off to demarcate sections that will create differences. Each tag will describe exceptions to transcluding the whole page named.

<pre>
<noinclude>  This section is visible here; but this section is not visible there. Sections outside of these tags will be visible both here and there. </noinclude>

<onlyinclude> This section is visible here; this section is also visible there. Sections outside of these tags will be visible here, but will not be visible there. </onlyinclude> 

<includeonly> This section is not visible here; but it is visible there. Sections outside of these tags will be visible both here and there. </includeonly></pre>
{| class="wikitable" style="text-align: center;"
! Wikitext
! What is rendered ''here'' (source page)
! What is transcluded ''there'' (destination page)
|-
|{{tag|noinclude|content=text1}} text2
|<code>text1 text2</code>
|<code>text2</code>
|-
|{{tag|onlyinclude|content=text1}} text2
|<code>text1 text2</code>
|<code>text1</code>
|-
|{{tag|includeonly|content=text1}} text2
|<code>text2</code>
|<code>text1 text2</code>
|}
An important point to note is that {{tag|noinclude|o}} and {{tag|onlyinclude|o}} do not affect what is page rendered ''here'' at all, unlike {{tag|includeonly|o}}. The {{tag|noinclude|o}} tags stops text inside the tags being transcluded ''there'', while {{tag|onlyinclude|o}} has the opposite effect: it stops text outside of the tags from being transcluded ''there''.

Only {{tag|includeonly|o}} stops text from being page rendered ''here''. But naturally enough it is transcluded ''there''. Text outside of the tags will be both rendered ''here'' and transcluded ''there''.

There can be several such sections. Also, they can be nested. All possible differences between ''here'' and ''there'' are achievable. 

One example is a content editor who picks an {{tag|onlyinclude|o}} section, and then takes a {{tag|noinclude|o}} section out of that; but then picks out yet another {{tag|onlyinclude|o}} section to append to ''there''; but none of this affects their article in any way.
 
Another example is the template programmer, who will {{tag|includeonly|o}} the code section and {{tag|noinclude|o}} the documentation section of a page.

==Selective transclusion==
{{shortcut|WP:SELECTIVETRANSCLUSION|WP:SELTRANS}}
{{See also|Template:Excerpt|Template:Transcluded section}}
''Selective transclusion'' is the process of [[#Partial transclusion|partially transcluding]] one selected section of a document that has more than one transcludable section.  As noted above, if only one section of a document is to be transcluded, this can be done by simply surrounding the section of interest with <syntaxhighlight lang="wikitext" inline><onlyinclude> … </onlyinclude></syntaxhighlight> tags, and transcluding the whole page.  However, to selectively transclude one section from a template or document into one page, and another section from the same template or document into a second page and/or a different section of the same page, requires a way to: 
:a) uniquely mark each transcludable section in the source document; and
:b) in the target document(s) (those to show the transcluded sections), a way to specify which section is to be transcluded.

This section describes how to accomplish this. There are three ways of doing this: (1) Section header-based transclusion, (2) Labeled section transclusion, and (3) the parametrization method.

===Standard section transclusion===
{{notice|text='''This method may cause line break insertion:''' Standard section transclusion may introduce a leading or trailing [[Line break (computing)|line break]] or newline, depending on the markup in the source and target pages. To prevent this, [[Wikipedia:Wrapper templates|wrap]] the transclusion code in a {{tlc|trim}} template. See [[#prevent line break insertion|examples below]].}}
Standard section transclusion uses <syntaxhighlight lang="wikitext" inline>{{#section-h:PAGENAME|SECTIONNAME}}</syntaxhighlight>. One can easily transclude the content within a section from one page to another using the ubiquitous headline-based [[Help:Section|section headers]] used throughout Wikipedia. To transclude the [[Wikipedia:Lead|lead]] section of an article with this method, one can use {{nowrap|<syntaxhighlight lang="wikitext" inline>{{#section-h:PAGENAME}}</syntaxhighlight>}}. This method is simpler than other selective transclusion methods, which require special [[Wikipedia:Markup|markup]] in the source article or page to specify what content should be included or excluded.

{{anchor|prevent line break insertion}}Standard section transclusion may introduce a leading or trailing [[Line break (computing)|line break]] or newline, depending on the markup in the source and target pages. To prevent this, [[Wikipedia:Wrapper templates|wrap]] the transclusion code in a {{tlx|trim}} template. For example:
* To transclude the section of an article: <syntaxhighlight lang="wikitext" inline>{{trim|{{#section-h:PAGENAME|SECTIONNAME}}}}</syntaxhighlight>
* To transclude the lead of an article: <syntaxhighlight lang="wikitext" inline>{{trim|{{#section-h:PAGENAME}}}}</syntaxhighlight>
<!-- This warrants expansion (better formatting, examples), but I'm creating the section for now - to see what the initial feeback is. -Elvey)-->

====Hatnote on the target page====
To indicate on the {{em|target page}} where selectively transcluded content originates (its source), a {{tlx|Transcluded section}} [[Wikipedia:Hatnote|hatnote]] must be placed at the top of the corresponding section in the {{em|target page}} where the content is being transcluded {{em|to}}.{{refn|group=lower-alpha|No hatnote should be placed on the {{em|source page}}, in other words no hatnote is needed on the page being transcluded {{em|from}}, as readers do not need to know where else the content appears.}}{{refn|group=lower-alpha|That is the hatnote should be placed below the header but above the content, per [[MOS:Layout]].}} Use either of the following, depending on whether the transcluded content is the entire section or only part of it:
* If an entire section in the target page is transcluded the source: <syntaxhighlight lang="wikitext" inline>{{transcluded section|source=PAGENAME#SECTION}}</syntaxhighlight>, which renders as:
:{{transcluded section|source=PAGENAME#SECTION}}
* If only part of a section in the target page is transcluded the source, specify {{para|part|yes}}: <syntaxhighlight lang="wikitext" inline>{{transcluded section|source=PAGENAME#SECTION|part=yes}}</syntaxhighlight>, which renders as:
:{{transcluded section|source=PAGENAME#SECTION|part=yes}}

====Hidden comment on the source page====

It is recommended to include a [[Wikipedia:Manual of Style/Hidden text|hidden comment]] at the beginning of the transcluded section in the {{em|source page}}. This comment informs editors that the content is being used elsewhere and serves as a reminder to consider the broader audience when modifying the wording. Additionally, it helps maintain the integrity of the transcluded material on the target page. For example (replace {{mono|<nowiki>[[PAGENAME#SECTION]]</nowiki>}} with the name of the target page):

{{Talk quote block minimalist|{{Example HTML comment|The content of this section is transcluded to <syntaxhighlight lang="wikitext" inline>[[PAGENAME#SECTION]]</syntaxhighlight>. Please be aware that changes made to the original source here will affect the transcluded version on the target page mentioned.}}}}

'''No hatnote should be placed on the {{em|source page}}''', in other words no hatnote is needed on the page being transcluded {{em|from}}, as readers do not need to know where else the content appears.

===Using the labeled section method===
{{main|Help:Labeled section transclusion}}
Labeled-section selective transclusion uses the [[WP:PF|parser function]]s listed in [[mw:Extension:Labeled Section Transclusion]], which are enabled on all Wikimedia wikis, to selectively transclude content. See [[Help:Labeled section transclusion]] for how labeled section transclusion works.

===Parametrization method===

=====Source document markup=====
Insert the following line into the "source" document (the one from which text is to be transcluded), immediately preceding the first line of each section to be transcluded, substituting SECTIONNAME (twice) with the unique name of the respective section. The section name can be any identifier and must be unique within that document:
:<syntaxhighlight lang="wikitext" inline><onlyinclude>{{#ifeq:{{{transcludesection|SECTIONNAME}}}|SECTIONNAME|</syntaxhighlight>
End each such transcludable section with:
:<syntaxhighlight lang="wikitext" inline>}}</onlyinclude></syntaxhighlight>

=====Target document markup=====
To transclude a section marked as above into another page (the "target page"), use the following line on that page, substituting PAGENAME for the "source" document from which text to be transcluded, and SECTIONNAME with the name of the section you want to transclude:
:<syntaxhighlight lang="wikitext" inline>{{PAGENAME|transcludesection=SECTIONNAME}}</syntaxhighlight>

Thus each section enclosed within <syntaxhighlight lang="wikitext" inline><onlyinclude> … </onlyinclude> </syntaxhighlight> tags will always be rendered when the <code>transcludesection</code> parameter is not set (when the document is viewed ordinarily, or when the document is transcluded without setting the <code>transcludesection</code> parameter as shown below), and will be rendered by transclusion on any page that does set <code>transcludesection</code> to the section's name.  It will ''not'' be rendered by transclusion that uses the <code>transcludesection</code> parameter but sets it to anything other than the name of the section.

Also, when providing PAGENAME, without providing a [[Wikipedia:Namespace|Namespace]], the wiki will assume that the PAGENAME belongs in the [[Wikipedia:Template_namespace|Template Namespace]]. To transclude from a [[Wikipedia:Main_namespace|Mainspace]] article, use :PAGENAME.

:<syntaxhighlight lang="wikitext" inline>{{:PAGENAME|transcludesection=SECTIONNAME}}</syntaxhighlight>

=====Example=====
If we want to make the "Principal Criteria" and "Common Name" sections of [[WP:TITLE]] be independently transcludable, we edit the WP:TITLE page and enclose the "Principal Criteria" section as follows:
<syntaxhighlight lang="wikitext">
<onlyinclude>{{#ifeq:{{{transcludesection|principalcriteria}}}|principalcriteria|
...
''(text of "Principal Criteria" section)''
...
}}</onlyinclude>
</syntaxhighlight>
Similarly, we enclose the "Common Name" section with:
<syntaxhighlight lang="wikitext">
<onlyinclude>{{#ifeq:{{{transcludesection|commonname}}}|commonname|
...
''(text of "Common Name" section)''
...
}}</onlyinclude>
</syntaxhighlight>
Then, to transclude the "Principal Criteria" section into another page, we insert into that page:
:<syntaxhighlight lang="wikitext" inline>{{WP:TITLE|transcludesection=principalcriteria}}</syntaxhighlight>

To transclude the "Common Name" section into another page, we insert into that page:
:<syntaxhighlight lang="wikitext" inline>{{WP:TITLE|transcludesection=commonname}}</syntaxhighlight>
Of course, the same page can transclude two or more sections this way by including multiple such lines.

There is no limit to how many selectable sections for transclusion a document can have.  The only requirement is that each <code>transcludesection</code> be given a value that is unique within that page.

=====Additional markup for selectively transcluded sub-article leads=====
{{further|Wikipedia:Summary style#Using excerpts for article synchronization}}

Per [[MOS:LEAD#Format of the first sentence]], the first instance of the sub-article title should appear in bold in the first lead sentence of that article; this is often not desirable for a transclusion to a section of the parent article. In addition, the parent article is often wikilinked in the lead of a sub-article; when transcluded to the parent article, this wikilink will appear as bold text.  The wikitext markup listed below can be used to address both of these problems.

To ensure that the article title is bolded in the first sentence of the sub-article, but unbolded and wikilinked in the transclusion to the parent article, make the following replacement in the sub-article's first lead sentence:
:Replace
::<code>'''{{var|SUB-ARTICLE_PAGENAME}}'''</code>
:with
::<syntaxhighlight lang="wikitext" inline><noinclude>'''</noinclude>{{No selflink|{{var|SUB-ARTICLE_PAGENAME}}}}<noinclude>'''</noinclude></syntaxhighlight>

If there is a wikilink to the parent article in the lead section of the sub-article, replacing the wikilink to the parent article with a {{tlx|no selflink}} template will ensure that it is wikilinked in the sub-article's lead but not in the transclusion to the parent article.  In other words:
# If the wikilink to the parent article is not a [[WP:Piped link]], replace <code>&#91;&#91;{{var|PARENT_ARTICLE}}&#93;&#93;</code> with {{tnull|no selflink|{{var|PARENT_ARTICLE}}}} in the sub-article's lead
# If the [[Wikipedia:Piped link|wikilink to the parent article includes a pipe (e.g., this link)]], replace <code>&#91;&#91;{{var|PARENT_ARTICLE}}|{{var|Piped link wikitext}}&#93;&#93;</code> with {{tnull|No selflink|{{var|PARENT_ARTICLE}}|{{var|Piped link wikitext}}}} in the sub-article's lead

==Drawbacks==
{{Shortcut|H:TRANSDRAWBACKS|}}
{{see|Wikipedia:Transclusion costs and benefits}}

Like many software technologies, transclusion comes with a number of drawbacks. The most obvious one being the cost in terms of increased machine resources needed; to mitigate this to some extent, [[Wikipedia:Template limits|template limits]] are imposed by the software to reduce the complexity of pages. Some further drawbacks are listed below.

*Transcluded text may have [[Wikipedia:Verifiability|no sources]] for statements that should be [[WP:BURDEN|sourced where they appear]],  have different [[WP:CITEVAR|established reference styles]],  contain [[Help:Cite errors/Cite error references no text|no-text cite errors]], or [[Help:Cite errors/Cite error references duplicate key|duplicate key errors]]. (To help mitigate these, see [[Help:Cite errors]])
*Excerpts break the link between article code and article output.
*Changes made to transcluded content often do not appear in watchlists, resulting in unseen changes on the target page. 
*Transcluded text may cause [[MOS:REFLINK|repeated links]] or have different [[MOS:ENGVAR|varieties of English]] and [[WP:DATERET|date formats]] than the target page. 
*Transclusions may not reflect [[Wikipedia:Protection policy|protection levels]], resulting in transcluded text perhaps having a different [[WP:PPLIST|level of protection]] than the target page. See [[WP:CASCADE|Cascading protection]]
*{{tl|excerpt}} and related templates may require using {{tag|noinclude|o}}, {{tag|includeonly|o}} and {{tag|onlyinclude|o}} markup at the transcluded page to have [[WP:SELECTIVETRANSCLUSION|selective content]]; that would require monitoring that the markup is sustained. 
*Excerpts cause editors to monitor transcluded pages for  "section heading"  changes to ensure transclusion continues to work. (To help mitigate this, see [[MOS:BROKENSECTIONLINKS]])
*Excerpts can result in content discussions [[WP:CROSS-POST|over multiple talk pages]] that may have different considerations or objectives for readers.

==Special pages==
{{see also|Wikipedia:Special pages#Miscellaneous}}

Some pages on [[Special:Specialpages]] can be transcluded, such as [[Special:AllPages|AllPages]], [[Special:PrefixIndex|PrefixIndex]], [[Special:NewFiles|NewFiles]], [[Special:NewPages|NewPages]], [[Special:RecentChanges|RecentChanges]], [[Special:WhatLinksHere|WhatLinksHere]] (see [[Help:What_links_here#Transclusion_of_WhatLinksHere|help page]]), and [[Special:RecentChangesLinked|RecentChangesLinked]].
Samples:
*<syntaxhighlight lang="wikitext" inline>{{Special:AllPages/General}}</syntaxhighlight> – a list of pages starting at "General".
*<syntaxhighlight lang="wikitext" inline>{{Special:PrefixIndex/General}}</syntaxhighlight> – a list of pages with prefix "General".
*<syntaxhighlight lang="wikitext" inline>{{Special:NewFiles/4}}</syntaxhighlight> – a gallery of the four most recently uploaded files.
*<syntaxhighlight lang="wikitext" inline>{{Special:NewPages/5}}</syntaxhighlight> – a list of the five most recently created pages.
*<syntaxhighlight lang="wikitext" inline>{{Special:RecentChanges/5}}</syntaxhighlight> – the five most recent changes.
*<syntaxhighlight lang="wikitext" inline>{{Special:RecentChangesLinked/General}}</syntaxhighlight> – recent changes to the pages linked from "General".
*<syntaxhighlight lang="wikitext" inline>{{Special:Contribs/Larry Sanger|offset=20021108002158|limit=50}}</syntaxhighlight> – user contributions prior to November 2002, limited to 50.

Attempting to transclude <syntaxhighlight lang="wikitext" inline>{{Special:Categories}}</syntaxhighlight> will not result in an actual list of categories, but <syntaxhighlight lang="wikitext" inline>{{Special:PrefixIndex/Category:}}</syntaxhighlight> can be used for this purpose.

Except for <syntaxhighlight lang="wikitext" inline>Special:RecentChangesLinked</syntaxhighlight>, the slash, and the word or number after the slash, can be omitted, giving a list of pages without a specific starting point, or a list of the default length.

[[Help:URL|URL]] parameters can be given like template parameters:
*<syntaxhighlight lang="wikitext" inline>{{Special:RecentChanges|namespace=10|limit=5}}</syntaxhighlight> – the five most recent changes in the "Template" namespace.
*<syntaxhighlight lang="wikitext" inline>{{Special:PrefixIndex/Jimbo Wales/|namespace=2|stripprefix=1}}</syntaxhighlight> – the subpages for [[User:Jimbo Wales]], but without the user page prefix.

''Note:'' Transcluding certain special pages (such as [[Special:NewPages]]) can change the [[Wikipedia:Page name|displayed title]] of the page.

== Advanced concepts ==
{{Main|Help:Advanced transclusion}}<!-- Temporary move of paragraph from lede of this help document to this subsection per discussion at talk (Help talk:Transclusion#Make sense of lede paragraph on parsing and HTML syntax fragments) until such time as [[Help:Advanced transclusion]] is created. Comment 2025-02-18. -->
Transclusion occurs before [[parsing]] and can emit syntax fragments, like HTML entities, to preserve them in the final render. The content being transcluded is processed and embedded before the target page is parsed and fully rendered. When transclusion happens at the HTML layer before parsing, it allows certain content – like syntax fragments such as [[character entity references]] like <code>&#x26;</code> and <code>mp;</code> or specific HTML components – to be inserted in their original form and preserved in the final render. However, this approach may cause pages to render incorrectly or violate the [[principle of least surprise]] for the reader.{{refn|group=lower-alpha|For example, if [[Whitespace character|whitespace]], tabs, and [[newline]] HTML code are preserved without parsing, the final page may display awkward spacing, misalignments, or unexpected breaks. This whitespace is usually added in the source code to improve readability for developers and isn’t intended to appear in the published content.}} It should be used sparingly when cleaner alternatives are not available. Emitting fragments of template syntax, such as opening braces (<code><nowiki>{{}}</nowiki></code>), is unlikely to re-parse correctly as template syntax in the target page, and it is unwise to rely on such behavior unless formally documented.<!--tested on an older MediaWiki, newer versions may re-parse correctly. Dated unknown. -->

== Notes ==
{{reflist|group=lower-alpha}}

==See also==
===MediaWiki transclusion===

* [[mw:Transclusion]]: a simple introduction (at MediaWiki).
* [[meta:Help:Embed page]]: gives basic information (at Meta-Wiki).
* [[Wikipedia:MediaWiki namespace]] 
** [[meta:Help:MediaWiki namespace]]: at Meta-Wiki.
* [[meta:Help:Variable]]: information on [[MediaWiki]] variables (at Meta-Wiki).
* [[Help:Labeled section transclusion]]: 
** [[mw:Extension:Labeled Section Transclusion]]: at MediaWiki.
** {{Slink|meta:Help:Template|Labeled section transclusion}}: at Meta-Wiki.

===Templates===
* [[Help:A quick guide to templates]]: a simple introduction.
* [[Help:Template]]: more detailed description.
** [[meta:Help:Template]]: help at Meta-Wiki. Links to various other guides in the lead.
** [[mw:Help:Template]]: a simple introduction at MediaWiki.
* [[Wikipedia:Template index]]: a directory of available templates.
* [[Wikipedia:Template namespace]]: about the template [[WP:Namespace|namespace]].
* [[Wikipedia:Template limits]]: limitations to complexity of pages.

===Other===
{{Wikipedia glossary}}
* {{tl|User transclusion}} and {{tl|User transclusion no}} – userboxes for declaring one's stance on transclusion
* [[Wikipedia:Purge]]: to force transclusion of newly updated templates.
* [[Wikipedia:Substitution]]: the opposite of transclusion.
* [[Wikipedia:WikiProject Modular Articles]]: now defunct.
* [[MediaZilla:4547|Bugzilla:Request for template transclusion from Commons]]: a proposal for interwiki template support.
* [[Mw:User:Peter17/Reasonably efficient interwiki transclusion]]
{{Portal templates navbox}}
{{Wikipedia technical help|collapsed}}
[[Category:Wikipedia editing]]
[[Category:Wikipedia page help]]
[[Category:Wikipedia template help]]