We need to document the $authenticated and $anonymous magic authz tokens
added in Subversion 1.5. 

Need to document the rule inversion syntax, too (also added in 1.5?). If my
code cruising is accurate, the following are all valid:

   [/some/path]
   ~cmpilato = rw        # Everybody except 'cmpilato' gets 'rw' permission.
   ~@group = rw          # Everybody except the 'group' group gets ... 
   ~$authenticated = rw  # Everybody not authenticated gets ... (same as
$anonymous?)