Confusion over the 3 merge forms

I have some merging questions:
 
According to the help for the svn merge command there are three forms:
usage: 1. merge sourceURL1[@N] sourceURL2[@M] [WCPATH]
           2. merge sourceWCPATH1@N sourceWCPATH2@M [WCPATH]
                       3. merge -r N:M SOURCE[@REV] [WCPATH]
 
The third form or Ranged Merging seems useful and is what we use here all
the time. I haven't seen forms 1 or 2 be of much use. I didn't even notice
them in the red bean book. Does any one know for what use case they were
designed?
 
 
Also, I am getting the request from my users that they'd like to not be
forced to remember which revisions they merged to a branch. I know that
branch tracking is a feature on the roadmap, but does anyone know if it is
possible to ask svn to just merge all changes from a branch to a mainline?
Basically, is there a way to say, make all changes flow from the branch to
the mainline if I do not know the appropriate revision range?
 
 

--
Peter Kahn
pkahn@connected.com