The MediaWiki software, which drives Wikipedia, allows the use of a subset of HTML5 elements, or tags and their attributes, for presentation formatting. But most HTML can be included by using equivalent wiki markup or templates; these are generally preferred within articles, as they are sometimes simpler for most editors and less intrusive in the editing window; but Wikipedia's Manual of Style recommends their use in certain cases. And HTML is useful outside of articles, for example for formatting within templates. For help with Cascading Style Sheet use within Wikipedia see Help:Cascading Style Sheets.

Is it true that in wikipedia it is possible to edit the text of an article in html.?
yes