-generating a linear patch stack. If such a stack cannot be generated,
-fail. This is the default for Debian.
+generating a linear patch stack: one new patch for each relevant
+commit.
+If such a stack cannot be generated, fail.
+This is the default for Debian.
+
+HEAD should be a series of plain commits
+(not touching debian/patches/),
+and pseudomerges,
+with as ancestor a patches-applied branch.