URLs that are enclosed in square brackets, but have a description following them, are displayed as a named reference within the document, as follows: ['tavi], [sourceforge].

You write them as follows. The URL must come first, followed by a space, followed by the text that describes the reference:

 [http://tavi.sourceforge.net/ 'Tavi]
 [http://www.usemod.com/cgi-bin/mb.pl Meatball]

And they appear like this:

['Tavi]
[Meatball]

See also FormalFormattingRules/Reference.