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 heading

<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.