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'''[[Transclusion]]''' means the inclusion of the content of one document in another document by reference. In Wikipedia, it refers to a function of the [[MediaWiki]] software that allows the content of one page to be included in the content of another page, by placing a reference to the source page in the [[WP:wikitext|wikitext]] of the target page. Changes made to a page are automatically reflected on all pages into which that page has been transcluded. A page that is intended to be transcluded into other pages is called a [[Help:Template|template]].
The basic syntax used to produce transclusion in wikitext is '''''<tt><nowiki>{{Namespace:Name}}</nowiki></tt>''''', which will be replaced by the content of the page named ''Namespace:Name'' when it is rendered on the user's display. If the referenced page name does not begin with a namespace identifier (''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:
* '''<tt><nowiki>{{Like}}</nowiki></tt>''' will transclude from the page [[:Template:Like]] - specifically: {{Like}}
* '''<tt><nowiki>{{Stochastic processes}}</nowiki></tt>''' will transclude from the page [[:Template:Stochastic processes]]
* '''<tt><nowiki>{{:Calculus}}</nowiki></tt>''' will transclude from the page [[Calculus]] (in the Main namespace)
* '''<tt><nowiki>{{WP:Assume good faith}}</nowiki></tt>''' will transclude from the page [[Wikipedia:Assume good faith]]
It is also possible to pass parameters to a template, using the expanded syntax described at [[Help:Template]], which can affect what text in the template is rendered. For example, to highlight text like {{highlight|this}}, the text-to-be-highlighted is passed as a parameter to the ''highlight'' template: <code><nowiki>{{highlight|this}}</nowiki></code>.
An alternative to transclusion is [[Help:substitution|substitution]], whereby the current content of the template is automatically copied into the wikitext of the target page on saving, and will then be an indistinguishable part of the saved page, independent of any later changes made to the template. The syntax for this is <code><nowiki>{{subst:Template name}}</nowiki></code>
==How transclusion works==
{{/How Transclusion Works}}
==Applications of transclusion==
The most common application of transclusion is in the use of [[Help:Template|templates]]. However, other pages are also sometimes transcluded, mainly within project space.
===Composite pages===
The wikitext of 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 the material on them into a central location.
Examples are:
*[[m:Help:A simple composite example]]
*[[Wikipedia:Village pump]] with six component pages, e.g. [[:Wikipedia:Village pump (technical)]]
*A daily page like [[Wikipedia:Votes for deletion/Log/2005 May 31]] where each component page consists of the discussion on the deletion of one Wikipedia page, e.g. [[Wikipedia:Votes for deletion/Sp3tt]] (for this day there are 75 such component pages)
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" link, 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, though 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 [[Help:Section#Editing sections of included templates|editing sections of included templates]]. After saving, one ends up at the page for the component page to which the section belongs.
On projects with the [[Help:Interwiki linking#Interlanguage links|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#transcluding prose]].
===Pages with a common section===
When two pages need to discuss the same material in the same way, they can share a section. This involves 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, and if the first it may be placed in the same namespace as the other pages or in template namespace. 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 [[WP:DAB|disambiguation]] pages share content, or a list page and a disambiguation page share content (see third example below)
Examples:
*{{pim|Help|Editing sections of included templates}}
*{{pim|Help|Alphabetic order}}
*[[Slough (disambiguation)]] transcludes [[Slough (hydrology)]], since the content of the former is nearly identical to one section of the latter.
===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:List of Languages]] calls [[Template:Lang def]] repeatedly with different parameters in order to generate the visible text.
Simple repetition of the same text can be handled with repetition of a parameter in a single template: e.g., {{tl|3x}}, where <nowiki>{{3x| howdy!}}</nowiki> produces {{3x| howdy!}}.
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==
By using "noinclude", "onlyinclude" and "includeonly" markup, it is possible to transclude part of a page rather than all of it. Such partial transclusions can also be achieved by transcluding from other pages such as subpages. It is often useful not to transclude some information, such as template documentation.
For an example of how this technique can be applied to simplify the creation of [[WP:SS|summary articles]], see how [[History of pathology]] [http://en.wikipedia.org/w/index.php?title=History_of_pathology&diff=prev&oldid=207668817] was transcluded into [[Pathology]],[http://en.wikipedia.org/w/index.php?title=Pathology&diff=prev&oldid=207669487] which consisted of a collection of transcluded [[WP:LEAD|lead paragraphs]] from several main articles.
{{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}}
There are three pairs of [[html element|tags]] involved in cases where rendering should differ between the [[wikitext]] and 1) its preview rendering, and 2) its transclusion rendering. Tags are the invisible [[HTML#Elements|elements]] that affect how a page renders.
Let's call a [[WP:preview|preview]] "rendered '''''here'''''", and a transclusion "rendered '''''there'''''".
A transcluded [[WP:page name|page name]] is ''no different'' than its preview.
But the tags pair-off to demarcate ''sections'' that will affect differences.
Each tag name will describe its invisibility ''exception'' to transcluding the whole page named.
:'''<nowiki><onlyinclude></nowiki>'''<tt>material outside this section</tt> invisible ''there'' '''<nowiki></onlyinclude></nowiki>'''
"Only" is not a term to reckon with because it means "only there" in the one, but "only this" in the other.
There can be several such sections. Also, they can be nested. All possible differences between ''here'' and ''there'' are achievable. The one example is a content editor who picks an onlyInclude section and takes a noInclude section out of that, picks out yet another onlyInclude section to ''append'' to ''there'', while none of this effects their article in any way. The other example is the template programmer who will includeOnly the code section and noInclude the documentation section of a page. A mis-example is the user page includeOnly section: it might "comment out" sections ''here'', but such [[invisible ink]] may prove to be troublesome, and transcluded the comments would be revealed commenting on nothing.
NoInclude as a name about transcluding is pretty straightforward.
A mnemonic for the other two transclusions ''there'' is: Inclusion''ONLY''; and ''Yet Another ONLY''Inclusion.
===Selective transclusion===
{{shortcut|WP:SELECTIVETRANSCLUSION|WP:SELTRANS}}
<b>Selective transclusion</b> 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 '''<tt><nowiki><onlyinclude> … </onlyinclude></nowiki></tt>''' 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 another 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.
====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:
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 '''<tt><nowiki><onlyinclude> … </onlyinclude> </nowiki></tt>''' tags will always be rendered when the '''<tt>transcludesection</tt>''' parameter is not set (when the document is viewed ordinarily, or when the document is transcluded without setting the '''<tt>transcludesection</tt>''' parameter as shown below), and will be rendered by transclusion on any page that does set '''<tt>transcludesection</tt>''' to the section's name. It will ''not'' be rendered by transclusion that uses the '''<tt>transcludesection</tt>''' 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.
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:
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 '''<tt>transcludesection</tt>''' be given a value that is unique within that page.
===Subpages===
One can cut and paste the text to be transcluded into a [[Wikipedia:Subpages|subpage]], then use the name of the subpage in the transclusion template. This approach can only be used with subpages from User, Talk or Wikipedia pages; currently, subpages [[Wikipedia:Subpages#Articles do not have sub-pages (main namespace)|cannot be created from main article pages]].
Example: you want to discuss the deletion and redirecting of [[Pussycat]] to [[Cat]]. First, create the subpage [[Talk:Pussycat/Let's delete Pussycat!]], write your comment into it, then transclude it in [[Talk:Pussycat]] and [[Talk:Cat]] using the template '''<nowiki>{{Talk:Pussycat/Let's delete Pussycat!}}</nowiki>'''. Comments posted in either talk pages will be shown in both. To ease editing of the subpage, it may be helpful to precede the transcluded talk with {{tl|lat}}, e.g. {{lat|Pussycat/Let's delete Pussycat!}}. Transcluding in this way will ''not'' preserve a fixed record of the discussion at the time of any archiving, so discussions should be closed in conjunction with archiving. An alternative is to centralise discussion in the normal manner on a single talk page and point to it using by [[WP:SUBST|substituting]] {{tl|Pls}} templates, per [[WP:MULTI]].
Some pages on [[Special:Specialpages]] can be transcluded, such as [[Special:Allpages]], [[Special:Prefixindex]], [[Special:Newfiles]], [[Special:Newpages]], [[Special:Recentchanges]] and [[Special:Recentchangeslinked]].
Samples:
*<nowiki>{{Special:Allpages/General}}</nowiki> – a list of pages starting at "General"
*<nowiki>{{Special:Prefixindex/General}}</nowiki> – a list of pages with prefix "General"
*<nowiki>{{Special:Newfiles/4}}</nowiki> – a gallery of the four most recently uploaded files
*<nowiki>{{Special:Newpages/5}}</nowiki> – a list of the five most recently created pages
*<nowiki>{{Special:Recentchanges/5}}</nowiki> – the five most recent changes
*<nowiki>{{Special:Recentchangeslinked/General}}</nowiki> – recent changes to the pages linked from "General"
Except for Special:Recentchangeslinked, the slash and the word/number after the slash can be omitted, giving a list of pages without a specific starting point, or a list of the default length.
'''Note:''' Transcluding certain special pages (such as [[Special:Newpages]]) can change the [[Wikipedia:Page name|displayed title]] of the page.
==Pages related to [[MediaWiki]] [[transclusion]]==