Each heading that you use generates also a "named anchor" into the HTML file. This allows you to refer to a section of a wiki page.
For example, if the heading on this page is called
!!This is my headingThe resulting HTML code would look like
<h3><a name="section-NamedHeadings-ThisIsMyHeading">This is my heading</a></h3>
This allows you to refer to the heading from a different wiki page using WikiMarkup!
For example, TextFormattingRules#PreformattedText refers to the "Preformatted text" -section of the page TextFormattingRules.
// code for link above [TextFormattingRules#PreformattedText]
If you are too lazy to figure out what the link name is, you can also just type the heading as-is: Text formatting rules#Preformatted text.
Note that this does not work with CamelCase links.