MediaWiki:Expand templates intro

This page takes some wikitext and expands everything in double braces recursively: templates, parser functions like {{#if:...}}, and variables like {{CURRENTDAY}}. A difference with recursive substitution is that the parameter default feature works. The preview section shows how the wikitext in the result section is rendered. This is typically, but not always, the same as how the wikitext in the input section is rendered.