understanding emacs packages

[knubee <knubee@gmail.com>]

This seems like it may be a faq, but I could not find the answer.

When I upgrade my gnu/linux distribution and re-install various emacs
applications, it is not always clear to me what is the cause of an
error when I run an emacs application. As an example, there may be
some oddness inserting dates in org-mode. No errors, but failure to do
things.

This could be because the gnu/linux distro is still in beta (e.g.,
ubuntu gutsy), it could be because I have  not installed all the
necessary emacs packages, or it could be because there non-emacs code/
application that is necessary.

So that is my question: how do different approaches to installing
emacs packages interact with packages in the existing emacs
distribution -- and interact with non-elisp applications?

Example: in the synaptic package manager, there is a "planner" package
and a "planner-el" package. When I select "planner-el" for
installation and "planner" is not required/suggested.

- Does this mean that "planner-el" is an elisp implementation of
"planner"?

- If so, are there cases where there is a "foo-el" package that relies
on a "foo" (non-elisp) application. In other words, can a situation
arise when I am using an application in emacs and it exhibits odd
behavior  because a non-emacs  application needs to be installed? If
so, is it always obvious?

And is there a straightforward way to tell if some package is already
part of the emacs distribution I am using (so that I do  not attempt
to download/install it myself)?

thanks for any help/pointers.