Our wikis use header styles which can be applied using the H1 button (rolling over this button will reveal H2, H3, H4, H5, and H6 as well)
These header styles allow us to both format and organize information on a wiki page. The wiki style gives predetermined attributes of font family, size, and weight, in addition to line height, to these different levels of header, with the H1 being the largest and H6 the smallest.
An additional benefit of using these headers is that the wiki can use them to automatically generate a table of contents for the page. After you have entered your text and formatted the titles that will act as headers to organize your information, place the cursor where you would like your table of contents to live and click the toc button.
The result will be the following code
Once you hit save, the wiki will find the various header text on your page and turn it into links to that text. These links will be nested like an outline based on the header style with H1 headers appearing farthest to the left and subsequent header levels further indented. Below is an example from the DML wiki with arrows pointing out the Table of Contents with listed and indented links. Beneath the TOC, arrows indicate the words Survey in style H2 and Fall '10 in style H3.