Help:Transclusion

Transclusion means the inclusion of the content of one document within another document by reference. In Wikipedia transclusion, the MediaWiki software will refer to the content of one page, the template, for inclusion into the content of any other page, the target page. Similar to the way any page name can become a link by placing its name in double square brackets, any page name can become a template by placing it in double curly braces,  . Changes made to the template are then automatically reflected on all pages into which that page has been transcluded (though a purge may sometimes be necessary).

If the template's page name does not begin with a namespace, it is assumed to be in the Template namespace. To refer to a page in the "Main" (article) namespace, it is necessary to prefix it with a colon (:). Examples:


 *   will transclude from the page Template:Stochastic processes
 *   will transclude from the page Stochastic processes (an article, in the Main namespace)
 *   will transclude from the page Assume good faith

What will transclude from a page can be controlled with the tags, and placed in the source page wikitext. (See markup, below.) The use of tags enables the template to transclude partially, otherwise the double curly braces will always transclude all content. For selective transclusion the parts of the template are named (with the help of parser functions) and that template is then called with the parameter.

Transclusion events occur every time the page is loaded, when the template is rendered. Another use of the same mechanism is a one-shot substitution of the template call itself by its transcluded source page. A template call  with the "subst:" prefix   is transcluded once but never again, because the wikitext of that call is replaced (substituted) when its page is saved. What was a one-time template call becomes the actual wikitext of the template at the time of its call.

Transclusion runs in advance of parsing the target page at the HTML layer, so it is possible to emit syntax fragments—even fragments of entity references, such as "&amp;a" and "mp;"—that will parse successfully as combined text in the target page. As a design idiom, this tends to violate the principle of least surprise, so it should be used sparingly, when cleaner solution paths do not present themselves. Emitting fragments of template syntax, such as a pair of opening braces, is unlikely to successfully re-parse as template syntax in the target page. Even if this worked, it would be unwise to depend upon this as supported behaviour, unless formally documented.

Additionally, it is possible to transclude content from Wikidata into other wikis.

Transclusion syntax
The general syntax for transclusion on Wikipedia is, where   describes the title of a Wikipedia page.

Using transclusion syntax requires some knowledge of page titles. On Wikipedia, non-article pages have titles with a visible namespace and pagename separated by a colon; for example, the page Tips has  as the namespace, and   as the pagename. But encyclopedic articles only have a visible pagename in their titles: for example the article Potato has  as the pagename, and the namespace, called main namespace, is not visible.


 * The wikitext  will transclude the page titled  . For example, if a page has the wikitext   in it, it will transclude the page Notability into it. Please note that   would do exactly the same thing, as   is a namespace alias, which is automatically translated by the Wikipedia servers to.
 * If the namespace is omitted, but the colon is included, like, the encyclopedic article   will be transcluded. For example,   will transclude the article Notability.
 * If both namepace and colon are omitted, like, the   will be transcluded. For example  , and also  , will both transclude the Template:Notability.

So, in summary, an example page having the wikitext  or   included, will transclude the   into that example page. But  will have a different effect: it will transclude the article. Also,  will transclude the page , for pages with titles of that format. You also have the option of using template parameters and transclusion modifiers.

Subpages
Subpages are pages separated with a "/" (a slash) from their 'parent' page. For a parent page with the name format, its subpage name would have the format. This feature is disabled in the main, file, and MediaWiki namespaces, but not on their corresponding talk namespaces.

To transclude a subpage:


 * The general syntax is.
 * On the parent page of a subpage, it is either the general syntax or.
 * For a template namespace page, it is either the general syntax or.
 * Article subpages are disabled on this wiki, but would otherwise be.
 * You also have the option of using template parameters and transclusion modifiers

For example, to transclude Template:Like/doc, it would be either  or. Note that subpage names are case sensitive, and  would not work.

Template parameters
The most common application of transclusion is the transclusion of templates. Templates are pages that are written with the prime objective of being included in other pages, either through transclusion or substitution. As shown above, the usual syntax for transcluding a template titled Template:Pagename is. However, some templates can also use parameters. Parameters are variables that can be given values (also termed arguments) that can be passed on to certain templates in order for them to work in different ways. Templates can either use no parameters, a fixed number of parameters, or a variable number of parameters. The number of parameters a template can use is from one upwards.

The exact syntax for using parameters with templates can vary greatly, depending on the actual template being used. But, for an example template titled Template:Pagename, which happened to use three parameters, the general form would be:

with each parameter being substituted with a, or a  , when used in practice. Notice that each parameter is separated with a vertical bar. Parameters that take the form  are called unnamed or positional parameters. Parameters that take the form   are called named parameters. With unnamed parameters, the first, second, third etc. parameters are equivalent to parameters '1', '2', '3' etc. in template documentation. Unnamed parameters must be in the correct order, and best placed before named parameters. An example of the syntax using the Template:Collapse top:

In this particular example, three parameters are used, but Template:Collapse top can actually use a variable number of parameters. and  are the values of unnamed parameters '1' and '2'; and   is the value of the named parameter.

For more details, see Help:Template. Also, see Template index for a list of links to available Main Namespace related templates (usually for encyclopedic articles); and other Namespace related templates (usually for non-article pages); there is also a search function. Template parameters are also used in the parametrization method of selective transclusion.

Substitution
Substitution has a similar double curly-bracket syntax, and its action is similar to transclusion. When you preview a page with substitution wikitext in it, its action is identical to transclusion. But when you save a page with substitution wikitext in it, it differs in that it substitutes that wikitext with the actual wikitext of the template.

For example, when  is saved, it would substitute that wikitext with the actual wikitext from the Template:Like. In practice, the main difference that this makes is that if an update happened to the wikitext of the Template:Like, it would not update any pages where  had already been saved.

Magic words
Magic words are not examples of transclusion. But some have a similar double curly-bracket syntax and action to transclusion. For example,  renders the Fullpagename of any Wikipedia page. Like templates, some magic words can also take parameters, which are separated using a colon ; for example.

Templates do exist for some magic words, for example Template:FULLPAGENAME; but these just invoke the related magic word if passing parameters using a vertical bar (|); for example like. But magic words parameters are best passed directly by using a colon, for example like, which bypasses any templates.

Transclusion modifiers
As discussed above, with the example, the   code alters the transclusion to substitution. This is a transclusion modifier, a type of specialist magic word for altering transclusion in some manner. Another example is, where the   (colon character) forces transclusion to the main namespace. There are additional transclusion modifiers such as,  ,  ,  , and. For more details on their usage, see. Also see the modified commands,   and   used for labeled section transclusion.

Applications of transclusion
The most common application of transclusion is in the use of templates. However, other pages are also sometimes transcluded, mainly within project space.

Composite pages
Composite pages consist, wholly or partly, of transcluded component pages. The wikitext of such a page may, partly or fully, consist of tags, for the inclusion of component pages. The component pages are usually not in the template namespace, and are often full pages in their own right. Composite pages are intended to gather them into a central location.

Examples of composite pages:
 * Village pump: mostly consists of the transcluded page Template:Village pump.
 * A daily page like Articles for deletion/Log/2005 May 31, where each component page consists of the discussion on the deletion of one Wikipedia page, e.g., Articles for deletion/Sp3tt. For this day, 75 component pages made up the composite page.
 * m:Meta:Translation/Coordination, mainly containing
 * m:Meta:Translation/Coordination/List/Meta
 * m:Meta:Translation/Coordination/List/Main

This allows the choice between viewing the component pages separately or together. Viewing a composite page is convenient when there are many small, related component pages, in that it allows an overview of all the components without the effort of following numerous links.

In general, each component page and the composite page are treated separately. While the actual changes on the component pages will be transcluded onto the composite page, the edit history, recent changes, page-watch settings, page protection, TOC, "what links here" links, and other features of the composite page do not reflect, or affect, the histories, watch settings, protection levels, what links here lists of the component pages. The composite page is a page in its own right. The talk page of a composite page is used to talk about the composition and the page in general, not the component pages; although it in turn could be a composite of the talk pages of the component pages.

Editing a section of a component page can be done directly from the composite page, see editing sections of included templates. After saving, one ends up editing the component page to which the section belongs.

On projects with the interlanguage link feature, the composite page shows the combined interlanguage links of all component pages, hence possibly multiple links for one language or even for one page.

See also Wikipedia talk:Template namespace/Archive 1.

Pages with a common section
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 on other pages. This may also involve creating a third page and transcluding that page onto both pages. This third page may be a page in its own right or a subpage of either of the other two – except in article space, where subpages are not allowed (see WP:SUB). The third page may be placed in the same namespace as the other pages or in template namespace – again, except for use in article space, where templates should not store article text (see WP:TG). Common sections like this should be marked with an explanatory header, 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.

This can be very useful when two disambiguation pages share content, or a 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 . 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.
 * 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.
 * 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 — various kinds of lists, usually — 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., 3x, where  produces.

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

For more information on the current template system, see Template namespace.

Partial transclusion
By using, and  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 summary articles, see how part of the History of pathology (see the diff here) was transcluded into Pathology (see the diff here) using the  markup. The Pathology article at that time (see here) mainly consisted of transcluded lead paragraphs and other sections from a number of articles. Look at the source to see how this was done. 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.

Markup
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 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, and. 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.

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

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.

This section is not visible here; but it is visible there. Sections outside of these tags will be visible both here and there. An important point to note is that and  do not affect what is page rendered here at all, unlike. The tags stops text inside the tags being transcluded there, while  has the opposite effect: it stops text outside of the tags from being transcluded there.

Only 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 section, and then takes a  section out of that; but then picks out yet another  section to append to there; but none of this affects their article in any way. Another example is the template programmer, who will the code section and  the documentation section of a page.

Selective transclusion
Selective transclusion is the process of 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  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
Using, one can easily transclude the content within a section on one page to another by referring to the standard, ubiquitous headline-based section headers used throughout Wikipedia. To transclude the lead of an article with this method, one can use. This is simpler than the already widely used selective transclusion methods of the sections below, which require special source document markup.

In other words, use the following modifications to the transclusion code listed immediately above:
 * Code for transcluding a section in the body of an article:
 * Code for transcluding the lead of an article:

Transcluded section hatnote
For the purpose of indicating where selectively transcluded article content is located, it is helpful to include a hatnote at the top of the corresponding section of the page being transcluded to; i.e., use either  or, depending upon whether the transcluded content is an entire section of the transcluding page. These templates render as follows:
 * renders as:


 * renders as:

No such hatnote is needed at the section being transcluded, since where else the content might appear is not of immediate interest to the reader. However, an HTML comment note between the heading and the transcluded content is probably pertinent so that editors are aware of the repurposing of the material and keep the broader audience in mind with changing the wording. Example:

End each such transcludable section with:

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:

Thus each section enclosed within  tags will always be rendered when the   parameter is not set (when the document is viewed ordinarily, or when the document is transcluded without setting the   parameter as shown below), and will be rendered by transclusion on any page that does set   to the section's name. It will not be rendered by transclusion that uses the  parameter but sets it to anything other than the name of the section.

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



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: Similarly, we enclose the "Common Name" section with: Then, to transclude the "Principal Criteria" section into another page, we insert into that page:

To transclude the "Common Name" section into another page, we insert into that page:

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  be given a value that is unique within that page.

Additional markup for selectively transcluded sub-article leads
Per MOS:LEAD, 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
 * with
 * with

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 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:
 * 1) If the wikilink to the parent article is not a WP:Piped link, replace   with  in the sub-article's lead
 * 2) If the wikilink to the parent article includes a pipe (e.g., this link), replace   with  in the sub-article's lead

Drawbacks
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, template limits are imposed by the software to reduce the complexity of pages. Some further drawbacks are listed below.


 * Transcluded text may have no sources for statements that should be sourced where they appear, have different established reference styles,  contain no-text cite errors, or 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 repeated links or have different varieties of English and date formats than the target page.
 * Transclusions may not reflect protection levels, resulting in transcluded text perhaps having a different level of protection than the target page. See Cascading protection
 * excerpt and related templates may require using, and  markup at the transcluded page to have 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 over multiple talk pages that may have different considerations or objectives for readers.

Special pages
Some pages on Special:Specialpages can be transcluded, such as AllPages, PrefixIndex, NewFiles, NewPages, RecentChanges, WhatLinksHere (see help page), and RecentChangesLinked. Samples:
 * – a list of pages starting at "General".
 * – a list of pages with prefix "General".
 * – a gallery of the four most recently uploaded files.
 * – a list of the five most recently created pages.
 * – the five most recent changes.
 * – recent changes to the pages linked from "General".
 * – user contributions prior to November 2002, limited to 50.

Attempting to transclude  will not result in an actual list of categories, but   can be used for this purpose.

Except for, 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.

URL parameters can be given like template parameters:
 * – the five most recent changes in the "Template" namespace.
 * – the subpages for User:Jimbo Wales, but without the user page prefix.

Note: Transcluding certain special pages (such as Special:NewPages) can change the displayed title of the page.

MediaWiki transclusion

 * Transclusion: a simple introduction (at MediaWiki).
 * meta:Help:Embed page: gives basic information (at Meta-Wiki).
 * 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.
 * : 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.
 * Template index: a directory of available templates.
 * Template namespace: about the template namespace.
 * Template limits: limitations to complexity of pages.

Other

 * Transclusion for Dummies
 * User transclusion and User transclusion no – userboxes for declaring one's stance on transclusion
 * Purge: to force transclusion of newly updated templates.
 * Substitution: the opposite of transclusion.
 * WikiProject Modular Articles: now defunct.
 * Bugzilla:Request for template transclusion from Commons: a proposal for interwiki template support.
 * Mw:User:Peter17/Reasonably efficient interwiki transclusion