+=item Interactive rebase
+
+With a laundered branch,
+one can do an interactive git rebase of the delta queue.
+
+=item New upstream rebase
+
+Start rebasing onto a new upstream version,
+turning C<...#..@-A-B-1-2-3> into C<(...#..@-A-B-, ...#'-)@'-1-2>.
+
+This has to be a wrapper around git-rebase,
+which prepares @' and then tries to rebase 1 2 onto @'.
+If the user asks for an interactive rebase,
+@' doesn't appear in the commit list, since
+@' is the newbase of the rebase (see git-rebase(1)).
+
+Note that the construction of @' cannot fail
+because @' simply copies debian/ from B and and everything else from #'.
+(Rebasing A and B is undesirable.
+We want the debian/ files to be non-rebasing
+so that git log shows the packaging history.)
+
+=item Stitch
+
+Make a pseudomerge,
+whose contributing parent is the unstitched branch
+and
+whose overwritten parent is ffq-prev,
+consuming ffq-prev in the process
+(and writing debrebase-last instead).
+Ideally the contributing parent would be a laundered branch,
+or perhaps a laundered branch with a quilt patch addition commit.
+
+=item Commit quilt patches
+
+To generate a tree which can be represented as a
+3.0 (quilt) .dsc source package,
+the delta queue must be reified inside the git tree
+in B<debian/patches/>.
+These patch files can be stripped out and/or regenerated as needed.
+
+=back
+
+=head1 ILLEGAL OPERATIONS
+
+Some git operations are not permitted in this data model.
+Performing them will break git-debrebase.
+
+=over
+
+=item General merges
+
+See L</OTHER MERGES>, above.
+
+=item git-rebase starting too soon, or without base argument
+
+git-rebase must not be invoked in such a way that
+the chosen base is before the anchor,
+or before the last pseudomerge.
+This is because git-rebase mangles merges.
+git rebase --preserve-merges is also dangerous.
+
+git-rebase without a base argument will often start too early.
+
+For these reasons,
+it is better to use git-debrebase and
+let it choose the base
+for your rebase.
+If you do realise you have made this mistake,
+it is best to use the reflog to recover to a suitable
+good previous state.
+
+=item Editing debian/patches
+
+debian/patches is an output from git-debrebase,
+not an input.
+If you edit patches git-debrebase will complain
+and refuse to work.
+If you add patches your work is likely to be discarded.
+
+Instead of editing patches,
+use git-debrebase to edit the corresponding commits.
+
+=item Renaming (etc.) branch while unstitched
+
+The previous HEAD,
+which will be pseudomerged over
+by operations like git-debrebase stitch,
+is recorded in a ref name dervied from your branch name.
+
+If you rename unstitched branches,
+this information can get out of step.
+
+Conversely,
+creating a new branch from an unstitched branch
+is good for making a branch to play about in,
+but the result cannot be stitched.