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Transclusion is generally the inclusion of the content of a document into another document by reference. In the Wikipedian context, it is the use of the template functionality of MediaWiki to include the same content in multiple documents without having to edit those documents separately.
How transclusion works
To transclude any source page (within a single MediaWiki project, such as en:Wikipedia) within another target page, include the following code:
{{SOMEPAGE}}
Whenever the target page A with this code is rendered, the engine will include in that place not the code itself, but the entire content of the source page B, SOMEPAGE.
For example, you might decide to place a welcome message on every newcomer's Talk Page. Transclusion creates a "live" link between the template-page and the target-page(s) upon which the message should appear. When the template is edited, all the target-pages are edited too.
For example, you might decide to create a (template) page with your mailing address and include that template on not only your page, but all your friends' pages, too. When you move your television and couch to another apartment, you will change your address template, and automatically, that new information will appear on all your friends' pages.
Etymology
Ted Nelson coined the term "transclusion," as well as "hypertext" and "hypermedia", in his 1982 book, Literary Machines.
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 summary articles, see Pathology, which consists of a collection of transcluded lead paragraphs from several main articles.
Transclusion markup
- noinclude. The markup <noinclude>...</noinclude> means that the text between the tags will not be transcluded onto another page, but will only appear on the page itself. This is useful for documentation.
- includeonly. The markup <includeonly>...</includeonly> means that the text between the tags will only be used when the page is transcluded onto another page, and will not appear on the page itself. This can be useful, for example, for adding categories to pages transcluding a template, without adding the template itself to these categories.
- onlyinclude. The markup <onlyinclude>...</onlyinclude> indicates that only text surrounded by "onlyinclude" markup should be transcluded onto another page. This is the most subtle of the partial transclusion tags because it often overrules the others. If there is at least one pair of "onlyinclude" tags on a page, then whenever this page is transcluded, it is only the material within the "onlyinclude" tags which gets transcluded. There can be several such sections, and within each such section, some material might be further excluded by "noinclude" tags, and might also be surrounded by "includeonly" tags so that it does not appear on the original page itself. But material outside the "onlyinclude" tags will be ignored when the page is transcluded onto another page. This can be useful, for example, to repeat a small part of one page on a second one: just surround the small part by onlyinclude tags, and transclude it onto the second page.
Templates
See also
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