Template:1/doc
 | This is a documentation subpage for Template:1. It may contain usage information, categories and other content that is not part of the original template page. |
 | This template may have no transclusions. This is because it is substituted by a tool or script, it is used as part of a short-term or less active Wikipedia process, or for some other reason. |
Templates {{1}}, {{2}}, {{3}}, etc. warn readers/editors that a typo exists in the page they are reading/editing. If {{1}} is called, you probably meant the parameter 1 (as {{{1}}} with triple braces), but in fact only double braces were used, invoking {{1}}. In addition to a warning, it also adds pages to Category:Templates with incorrect parameter syntax. For more information on how template parameters work, see mw:Help:Templates#Parameters.
However, the most problems have been caused by omitting the first brace "{" of a parameter and getting {{1}}}, as invoking Template:1 +"}" rather than parameter 1. This can be an insidious problem, especially when the transclusion of Template:1 is hidden, so that the effect is invisible to the person editing a page. For that reason, Template:1 now issues a warning to the user.
With that warning, the prior invisible access to Template:1 can now be understood to be a formerly unseen problem coded within a page.
Note: this will also pick up several variations such as {{1|}} for {{{1|}}} and {{{1}}.
Periodically, people check what-links-here to see if anyone has accidentally invoked Template:1.