Help:Variables
From Apache OpenOffice Wiki
See: Extension:VariablesExtension
Variables is a very simple MediaWiki extension that allows you to define a variable on a page, use it later in that same page, change its value, possibly to a value given by an expression in terms of the old value, etc.
See Extension:VariablesExtension#Assigning_a_value_to_a_variable for documentation and examples showing how to use this extension.