GeezerVison

Consider an example, complemented by the illustration below, with target pages A, P, and Q, and source page B.

If source page B is transcluded into A, the content from B (for instance, the word "foo") will appear in place of the {{B}} code in page A. When transcluded, this content is not highlighted or boxed on the target page – it is integrated directly into the page's text (highlighted here only for illustration).

Transclusion creates a 'live' link between a source page and all target pages where its content is transcluded to and used. Editing the source page automatically updates its content on all target pages that include it.

For example, if you create a source page with details about a Wikimedia event and transclude it onto the talk pages of 50 editors you wish to invite, any updates you make to the source page (such as changing the event location) will immediately reflect on all 50 talk pages.

Edits to a source page can impact all target pages using it. If a source page also contains its own transclusions from other source pages, avoid changes that may break these links, as this would affect the source page you are editing and all target pages that transclude it. This is known as 'breakage', and it is best to ensure any updates maintain the integrity of transcluded content across all pages. For example, Main Page is a large page that transcludes its content from multiple embedded source pages such as Wikipedia:Today's featured list.

• Specifying namespace: {{Namespace:Pagename}} will transclude the page titled Namespace:Pagename. For example, if a page has the wikitext {{Wikipedia:Notability}} in it, it will transclude the page Wikipedia:Notability into it. Please note that {{WP:Notability}} would do exactly the same thing, as WP: is a namespace alias, which is automatically translated by the Wikipedia servers to Wikipedia:.
• Calling from the Article namespace: If the namespace is omitted, but the colon is included, like {{:Pagename}}, the mainspace article Pagename will be transcluded. For example, {{:Notability}} will transclude the article Notability.
• Template namespace: If both namespace and colon are omitted, like {{Pagename}}, the Template:Pagename will be transcluded. For example {{Notability}}, and also {{Template:Notability}}, will both transclude the Template:Notability.

Additionally, specific § Template parameters and § Transclusion modifiers allow parameters to be passed to templates, alter how transclusion occurs, and therefore the output customized. This is explained in more detail below.

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

To transclude subpages:

• In general, use {{Namespace:Pagename/Subpagename}}. With exception:
  • On the parent page of a subpage, the more specific general syntax mentioned above can be used or simply {{/Subpagename}}.
  • For a template namespace page, it is either the general syntax or {{Pagename/Subpagename}}.
  • Article subpages are disabled on this wiki, but would otherwise be {{:Pagename/Subpagename}}.
• Alternatively, you can also use § Template parameters and § Transclusion modifiers.

For example, to transclude Template:Like/doc, you could use {{Template:Like/doc}} or {{Like/doc}}. Note that subpage names are case sensitive, and {{Like/Doc}} would lead to a different page.

The most common use of transclusion on Wikipedia is for templates. Templates are specially designed pages intended to be included in other pages using either transclusion or substitution. The standard syntax for transcluding a template titled Template:Pagename is {{Pagename}}.

Additionally, many templates support parameters, which are variables that allow templates to function in different ways by passing specific values, also termed 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 Template:Pagename that accepts three parameters, the general format would be:

{{Pagename|parameter1|parameter2|parameter3}}

Where each parameter in a template can be substituted with either a value or a |parameter name=value format when used in practice. Notice that each parameter is separated by a vertical bar (|). Parameters that take the form value are called unnamed or positional parameters, while those in the form |parameter name=value are known as named parameters. With unnamed parameters, the first, second, and third parameters correspond to |1=, |2=, |3=, respectively, etc., in template documentation. Unnamed parameters must be provided in the correct order and are best placed before named parameters.^[d]

For example, using the Template:Collapse top with two unnamed parameters and one named parameter:

In this case, This is the title text and This is a custom warning line are the values of unnamed parameters |1= and |2=, while true is the value assigned to the named parameter |left=. The last example shows how unnamed parameters should not be used after named parameters without their 'name'. Although this example includes three parameters, 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 § Parametrization method of § Selective transclusion, allowing for more dynamic content inclusion.

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 {{Pagename}} with the subst: prefix results in the substitution template call {{subst:Pagename}}. 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.^[e]

For example, when {{subst:Like}} is inserted in a page and the changes published, it would substitute that wikitext with the actual wikitext from Template:Like. In practice, subsequent updates to Template:Like will not be reflected in the page it was substituted into.

Magic words are not examples of transclusion. But some have a near identical double curly bracket syntax and similar action to transclusion. For example, {{FULLPAGENAME}} renders the full page name of any Wikipedia page, for example it returns Help:Transclusion on this page. Like templates, some magic words can also take parameters, which are separated using a colon (:); for example {{TALKPAGENAME:Help:Transclusion}} returns Help talk: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 vertical bar (|) to the magic word in anycase; for example like {{FULLPAGENAME|value}}. But magic words parameters are best passed directly by using a colon, which bypasses the unnecessary use of a template call too. For example, {{FULLPAGENAME|value}} is synonymous with {{FULLPAGENAME:value}}, where the latter is preferred.

A transclusion modifier is a type of specialist magic word for altering transclusion in some manner. An example of which is the subst: modifier discussed above in § Substitution. Another example is {{:Notability}}, where the colon character (:) forces transclusion to the main namespace. There are additional transclusion modifiers such as safesubst:, int:, msg:, msgnw:, and raw:. For more details on their usage, see mw:Help:Magic words § Transclusion modifiers. Also see the modified commands #section:, #section-x: and #section-h: used for labeled section transclusion, see Help:Labeled section transclusion and the section § Using the labeled section method.

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 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.

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 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 article text, as this makes it more difficult to edit the content (see Wikipedia:Template namespace). Common sections like this should be marked with an explanatory header, such as using the templates {{transcluding article}} or {{transcluded section}} to create 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 disambiguation pages share content, or a list page and a disambiguation page share content (see second example below).

Examples:

• m:Help:Alphabetic order (talk, backlinks, edit)
• 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.

On pages with a lot of repetitive information – typically lists or tables – it can be useful to create a template that contains the repeating text, and then call that template multiple times. For example, {{EH listed building row}} is used repeatedly to build tables in many articles.

For simple repetition of the same text, you can use a template like {{3x}}. For instance, {{3x|howdy!}} produces: howdy!howdy!howdy!

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. 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 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 <noinclude>, <includeonly> and <onlyinclude>. 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.

<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>

An important point to note is that <noinclude> and <onlyinclude> do not affect what is page rendered here at all, unlike <includeonly>. The <noinclude> tags stops text inside the tags being transcluded there, while <onlyinclude> has the opposite effect: it stops text outside of the tags from being transcluded there.

Only <includeonly> 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 <onlyinclude> section, and then takes a <noinclude> section out of that; but then picks out yet another <onlyinclude> section to append to there; but none of this affects their article in any way.

Another example is the template programmer, who will <includeonly> the code section and <noinclude> the documentation section of a page.

This method may cause line break insertion: Standard section transclusion may introduce a leading or trailing line break or newline, depending on the markup in the source and target pages. To prevent this, wrap the transclusion code in a {{trim}} template. See examples.

This method does not work if the target is using hidden anchors: If the target section title contains hidden anchors using <span class="anchor" id="AnchorId"/> tags inside the section header, this header-based transclusion will not work as it assumes the entirely of the section title (including such "invisible" anchor spans. In such a case, use use the labeled section method instead.

Standard section transclusion uses {{#section-h:PAGENAME|SECTIONNAME}}. One can easily transclude the content within a section from one page to another using the ubiquitous headline-based section headers used throughout Wikipedia. To transclude the lead section of an article with this method, one can use {{#section-h:PAGENAME}}. This method is simpler than other selective transclusion methods, which require special markup in the source article or page to specify what content should be included or excluded.

Standard section transclusion may introduce a leading or trailing line break or newline, depending on the markup in the source and target pages. To prevent this, wrap the transclusion code in a {{trim}} template. For example:

• To transclude the section of an article: {{trim|{{#section-h:PAGENAME|SECTIONNAME}}}}
• To transclude the lead of an article: {{trim|{{#section-h:PAGENAME}}}}

Labeled-section selective transclusion uses the parser functions listed in mw:Extension:Labeled Section Transclusion, which are enabled on all Wikimedia wikis, to selectively transclude content. See Help:Labeled section transclusion for more details on how labeled section transclusion works.

Short instructions:

• On the page you wish to transclude text from:
  • On the target section you wish to transclude, add a <section begin="YourSectionLabel" /> at the start of the section
  • Followed by your normal text of the section
  • At the end of the section, place a <section end="YourSectionLabel" />
• On the page you want to add the transclusion to:
  • Place: {{#section:page name|YourSectionLabel}}

• 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.
  • meta:Help:Template § Labeled section transclusion: at Meta-Wiki.

• 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 namespace.
• Wikipedia:Template limits: limitations to complexity of pages.

This page is referenced in the Wikipedia Glossary.

• {{User transclusion}} and {{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.
• Cross-Wikimedia inclusion (interwiki templates transclusion, etc.) unsupported: a proposal for interwiki template support.
• Mw:User:Peter17/Reasonably efficient interwiki transclusion