As seen on
http://lists.osuosl.org/pipermail/darcs-users/2009-March/018053.html

Quick summary of the email thread:

No one wants to change the default no-conflicts for push, some even 
argue for making it the default for pull (they may have a point, but 
this is another issue). All participants except one argue for adding 
the flags as (non-default) options to push. Rationale: (1) if you 
explicitly say you want to allow conflicts you must know what you are 
doing; (2) there are certain work flows where going to the other repo 
and pulling from there is inconvenient or even difficult.

When darcs refuses to push because it would lead to conflicts, darcs 
suggests the --mark-conflicts option. Although the hint is for 'apply' 
command, it is nevertheless confusing. I was certainly surprised by 
the interaction listed below, even though I have been routinely using 
darcs for years. One tends to pick out "use the --mark-conflicts 
or --allow-conflicts options" from the text and ignore the details. We 
are only humans after all...

ben@sarun[1]: .../seq/2-0-98 > darcs push ../work 
The remote repository has 4 patches to pull.
Thu Mar  4 10:13:16 CET 2010  benjamin.franksen@bessy.de
  tagged R2-0-12
Shall I push this patch? (1/15)  [ynWvplxdaqjk], or ? for help: a

darcs failed:  Refusing to apply patches leading to conflicts.
If you would rather apply the patch and mark the conflicts,
use the --mark-conflicts or --allow-conflicts options to apply
These can set as defaults by adding
 apply mark-conflicts
to _darcs/prefs/defaults in the target repo. 
Backing up ./configure/RELEASE(-darcs-backup0)
There are conflicts in the following files:
./configure/RELEASE
Apply failed!
ben@sarun[1]: .../seq/2-0-98 > darcs push ../work --mark-conflicts

darcs failed:  unrecognized option `--mark-conflicts'

ben@sarun[1]: .../seq/2-0-98 > darcs push ../work --allow-conflicts

darcs failed:  unrecognized option `--allow-conflicts'

rather natural name would be --force which ensures that no matter what
the local version will be pushed to remote repo

god writes:
 > 
 > god <god12@niksula.hut.fi> added the comment:
 > 
 > rather natural name would be --force which ensures that no matter what
 > the local version will be pushed to remote repo

Except that AFAIK you can't ensure that a *version* is pushed in
Darcs, because Darcs is not DAG-based.  You can only ensure that the
local set of patches is a subset of the remote, but of course then you
may have a conflict which needs to be resolved by hand AFAIK -- you
can't just check out the desired version.