Table of contents
MediaWiki relies a great deal on HTML markup. Subscript, superscript, monospace, line breaks, ...
Due to the various edit plugins and the ability to use CSS classes to style the various tags, there's absolutely no need to resort to HTML.
HTML is disabled in this wiki.
Line break handling in MediaWiki is quite elaborate - see Wikpedia - Line Break Handling
It usually requires extra line breaks and/or the <br /> tag.
When you make a line break, you get a line break. It's that simple.
No need to make double line breaks or use the <br /> tag.
-= Titlebar =-
! Level 1
!! Level 2
!!! Level 3
!!!! Level 4
!!!!! Level 5
[[a link|with title]]
((a link|with title))
[http://example.org The title]
They are not really needed, as it's much faster and more flexible to use the DIV and BOX tags.
You can use styles - take a look at Wiki Styles.