RE: running multiple Emacs versions

[Drew Adams]

> Drew---
> 
> Regarding .elc files, aren't most of these placed in the individual
> App directories on Mac OS X, i.e. Aquamacs.app, Emacs.app?

I have no idea.

In the GNU Emacs distributions I use, the distributed *.elc files are in
directory `lisp' or one of its subdirectories. `lisp' itself is in the directory
where Emacs is installed.

> When you refer to "byte compiling", do you mean Emacs LISP
> packages you have written, or are you talking about installing
> external packages say from Elpa?

Most of what I wrote was about "byte-compiled" files, which includes those
distributed by GNU. It doesn't matter who byte-compiled a file, what kind of
*.el file was byte-compiled, or where the *.elc is stored. My point was about
compatibility among different Emacs versions with respect to byte-compiled
files.

When I spoke of byte-compiling files myself, I meant any files for which I have
a *.el and no *.elc or a *.el that is more up-to-date than the *.elc. That
includes files I've written and files from others. (I don't modify the files
distributed with Emacs, so I don't need to byte-compile them again.)

The main points were:

1. You can generally use a *.elc produced (byte-compiled) using an older Emacs
version.

2. You can use `emacs-major-version', `(require ... nil t)' or `featurep',
`fboundp', and `boundp' to check which version of Emacs, a feature, a function,
or a variable you are using.