how-to:
1. highlight the link text
2. press cmd-6/alt-6, it brings up a menu
3. choose one of the following:
   Link to comment of class
   Link to definition of class
   Link to hierarchy of class
   Link to method
   be a web URL link

examples:
1. simple web URL link:
   enter the URL 'http://www.squeak.org/'
   highlight it
   choose 'be a web URL link'
2. web URL with a descriptive text:
   enter the URL 'Squeak<http://www.squeak.org/>'
   highlight it
   choose 'be a web URL link'
3. link to a method
   enter 'Url asUrl' (or 'Url class quickieTest')
   highlight it
   choose 'Link to method'
4. link to a class definition
   enter 'Definition for class URL<Url>'
   highlight it
   choose 'Link to definition of class'