Help:Transclusion: Difference between revisions

'''Transclusion''' means the inclusion of the content of one document within another document by [[Reference (computer science)|reference]].  In Wikipedia transclusion, the [[MediaWiki]] software will refer to the content of one page, the [[WP:template|template]], for inclusion into the content of any other page, the target page.  Similar to the way any [[wp:page name|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, '''<syntaxhighlight lang="wikitext" inline>{{Namespace:Pagename}}</syntaxhighlight>'''. Changes made to the template are then automatically reflected on all pages into which that page has been transcluded (though a [[Wikipedia:Purge|purge]] may sometimes be necessary).

If the template's [[WP:page name|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:

Transclusion events occur every time the page is ''loaded'', when the template is rendered. Another use of the same mechanism is a one-shot ''[[Help:substitution|substitution]]'' of the template call itself by its transcluded source page.  A template call <code>{<nowiki/>{''[[WP:page name#Namespace, pagename, and fullpagename|fullpagename]]''}}</code> with the "subst:" prefix <syntaxhighlight lang="wikitext" inline>{{subst:fullpagename}}</syntaxhighlight> 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.

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

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

''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'''''.

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.

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:

# 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

*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]])

*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 can result in content discussions [[WP:CROSS-POST|over multiple talk pages]] that may have different considerations or objectives for readers.

* [[Wikipedia:Template namespace]]: about the template [[WP:Namespace|namespace]].