Link to an external webpage without showing the link: write the url in square brackets: [L1 ]. This is nice for really long links like [L2 ] - Amazon: "Practical Programming in Tcl and Tk (4th Edition)"
Link within the wiki to a specific wiki page: put name of page in square brackets: How do Wiki Categories work
Link within the wiki to a specific wiki page, showing square brackets: [Wikit Problems] - use triple square brackets
Link within the wiki to a wiki page, without getting a backlink: http://wiki.tcl.tk/2272 = [Category Application]