Can't understand usage of 'cvs admin -bxxx .',desiring for help.

[Lazy Dumbness]

13.3 Reverting to the latest vendor release 
You can also revert local changes completely and return to the latest vendor 
release by changing the `head' revision back to the vendor branch on all files. 
For example, if you have a checked-out copy of the sources in `~/work.d/wdiff', 
and you want to revert to the vendor's version for all the files in that 
directory, you would type: 

        $ cd ~/work.d/wdiff
$ cvs admin -bWDIFF .
Up is a section of CVS manual.I can't understand it really.first,it said that 
'if you have a checked-out copy of sources...',what is the release reverion of 
this source?As an example,I have a third-party sources with two release 
reversion named soft-1.0 and soft-1.1first,I import soft-1.0 like this:cvs 
import -m"1.0" soft company release1and then I checked the source and modified 
some file.cvs checkout soft//Modified some file for my own purpose and 
checkin.It seemed my checkin is the 'HEAD' trunk.Now the official release the 
new release soft-1.1.To recored it:cvs import -m"1.1" soft company 
release2OK,problem occurs.the cvs noticed:cvs import -m "111" my upidea 
release2C my/a.c1 conflicts created by this import.Use the following command to 
help the merge:        cvs checkout -j<prev_rel_tag> -jrelease2 myIf I want use 
new release and want new release merged my own modify.I'm sure I may do like 
upon.But if I want lost all my modifed for my ownproblem is solved in the new 
rel!
 ease and much more perfect than I do.So it seemed I shoud "reverting to the 
lastest vendor release",is this right?And I think what I shout do is.cvs 
checkout -r release2 softcvs admin -brelease2 .Here the cvs told me:cvs admin: 
Administrating .RCS file: /home/dumb/cvsroot/my/a.c,vcvs admin: 
/home/dumb/cvsroot/my/a.c,v: Symbolic name release2 is undefined.cvs admin: RCS 
file for `a.c' not modified.The manual use a command 'cvs admin -bWDIFF .' to 
explain this.I don't know what the 'WDIFF' means and where it come from?It's 
shout be anreversion.But in the manual it not said where the symbolic name 
WDIFF came from.I have no idea about this.Can somebody help?Thanks a lot.