} thanks Greg - can I clarify a couple of things please:
}
} re d) "The right way to handle this is with subversion and svnmerge" - given
} I've already been using the plugin install method is there a way to migrate
} to the approach you're suggesting? or should I just rename my plugin
} directories as a minimum to avoid the possibility of an accidental plugins
} update overwritting my changes?
I'm assuming that you are asking this question because you actually are
using subversion to manage your project, since otherwise it doesn't make
sense to ask. In that case, what you should do is the following:
1) Check out your modified version of the plugin somewhere handy so you'll
be able to compare it to the current version of the plugin.
2) In a working copy of your project, svn remove your plugin.
3) In that same working copy, svn copy the plugin from its repository and
commit. (You may want to do all this in a branch if having the
unmodified plugin in your project repository will cause things to break
for other people.)
4) Prepare for merging with svnmerge init in the plugin directory. Commit
again.
5) Diff your modified version you checked out in step 1 with the copied
version.
6) Port your changes to the to the copied version, make sure things are
working as expected, and commit.
When you want a new version of the plugin, you'll use svnmerge merge to get
it. If there's some change you don't like, find out which revision it was
in and svnmerge block it, then merge.
} re c) "classloading" - it would be great to have some sort of flowchart or
} cheat sheet that summarises how rails/ruby class loading works, and
} references various rails specific aspects such as: plugin aspects (init.rb's),
} engine, application.rb, environment etc etc. Do you know if such a thing
} exists - just asking as you seem to understand this area 
The automatic loading of classes/modules occurs in the const_missing
method, which Rails redefines. If you refer to a class/module that has not
been loaded yet, const_missing is called with the constant. For example,
suppose you have a module Foo::Bar::Baz and even the Foo namespace has not
been loaded. The const_missing method is called on Object with "Foo" and it
tries to require 'foo' first. If it succeeds, it's done, though if loading
that file didn't define Bar then const_missing will be called on Foo with
"Bar" next. If it fails, it will check to see if there is a directory named
'foo' in the $LOAD_PATH and, if so, create the Foo module and return. It's
all based on the $LOAD_PATH, though, so if there are multiple foo.rb files
in different parts of the $LOAD_PATH you can tell which one will be read by
where its location appears in the $LOAD_PATH (p it from script/console).
} Many Thanks
} GregH
--Greg