 | This page documents an English Wikipedia editing guideline. Editors should generally follow it, though exceptions may apply. Substantive edits to this page should reflect consensus. When in doubt, discuss first on this guideline's talk page. |
 | This page in a nutshell: Substitution is the one-time, permanent copying of template content on Wikipedia. It differs from transclusion, which continually updates as the linked-to content changes. |
Substitution is a different way of handling templates than normally done on Wikipedia. Usually, templates are transcluded, which means that if the template changes, every page that uses it will update to comply with the change-in-question. This is the procedure used for most templates. However, some templates are instead substituted. This means that if the template changes, the page that uses it will not, and will continue to show the old version of the template. Some templates should always be substituted, while most should always be transcluded.
To substitute, add subst: after the opening braces, as in {{subst:page name}}. For example: substitution {{subst:Medicine}} in contrast to transclusion {{Medicine}}. The contents of Template:Medicine will be expanded (for any templates) and stored at each point where "{{subst:Medicine}}" is placed in a page. Note that ref tags refuse to run "subst:" unless temporarily renamed as "<xref name=xx>" or similar (see the bug report at T4700).
This page also lists templates that should either always or never be substituted except in the Wikipedia namespace. Automated tools (a.k.a. bots) that do such replacements will never be used on the original template. If you are going to use a bot to substitute templates, please read through the talk page first, as many are under dispute or change status over time, and substitution is permanent.