ParserFunctions - Mediawiki
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The MediaWiki extension ParserFunctions is a collection of parser functions (note the difference between the name of the collection, and the general term). These parser functions have a hash character in front of the function name, so they typically have the syntax:
{{ #functionname: argument 1 | argument 2 | argument 3...}}
See http://meta.wikimedia.org/wiki/WM:PF for a complete description of functionality and syntax.
Example:
{{ #time: "The month is" F }} → The month is November