[gentoo-pms] Variancy?

[Ulrich Mueller <ulm@gentoo.org>]

Hi,
I don't understand the following passage from section "The state of
the system between functions":

  * Variancy is any package manager action that modifies either ROOT
    or / in any way that isn't merely a simple addition of something
    that doesn't alter other packages. This includes any non-default
    call to any pkg phase function except pkg_setup, a merge of any
    package or an unmerge of any package.
  * As an exception, changes to DISTDIR do not count as variancy.
  * The pkg_setup function may be assumed not to introduce variancy.
    Thus, ebuilds must not perform variant actions in this phase.

Why is the second item needed? Changes to DISTDIR don't alter other
packages, so aren't they covered by the first item anyway? Or do I
misunderstand the first item's first sentence?

Which of the following examples count as "variancy"?
  - Calling enewuser() in pkg_setup,
  - Removing orphan files in pkg_setup,
  - Calling pkg_pretend.

Ulrich