Template:!/doc
{{doc}}
Documentation
This provides a literal "pipe" character (|) in contexts where it would otherwise be interpreted as part of wiki markup syntax (e.g., in wikilinks, tables, and templates).
The template is actually not called if {{!}} is used, because that exact string is handled "natively" by MediaWiki. However, there are ways of forcing a call to the template (as seen in the examples below), and in those cases any input to the template is ignored.
The only thing the template does, in fact, is output (the value of) {{!}}, so really the only reason this template page exists is to document the use of the built-in feature.
Usage
{{!}}
Examples
{{!}}⇒ |{{!|}}⇒ |{{Template:!}}⇒ |
The first example uses the built-in feature; the second and third actually call this template. (In the second example, empty input is being passed to the template in the first unnamed/positional parameter — which is ignored, anyway). All three examples are totally equivalent in terms of their effects, except the first is a bit more efficient than the other two.