Learn more about Wikitext
There is no commonly accepted standard Wikitext language. The grammar, structure, features, keywords and so on are dependent on the particular wiki software used on the particular website. For example, all wikitext markup languages have a simple way of hyperlinking to other pages within the site, but there are several different syntax conventions for these links. Many wikis, especially the earlier ones, use CamelCase to mark words that should be automatically linked. In many modern wikis (such as Wikipedia and other MediaWiki-based wikis) this convention was abandoned in favor of explicit link markup, e.g. with [[…]].
Some Wiki programs allow extensive optional use of HTML tags within wikitext, others a smaller subset, and still others no HTML at all. In some cases, restrictions on HTML may be determined by each site that uses the program. It is now actually considered poor etiquette on wiki websites to use HTML in place of wiki markup, despite the former option being available.
MediaWiki, the software that runs Wikipedia, has a wiki markup language that allows many common HTML tags; it is intended to provide a simple, readable syntax to allow users to use it without knowing HTML.