Didier Verna <verna(a)inf.enst.fr&gt; writes in xemacs-beta(a)xemacs.org: Ah. A vocabulary gap. The only silly questions are those left unasked in the proper forum. No. The term "dumped" refers to those lisp packages that are loaded between the time temacs runs and the time the xemacs binary gets written out. This means various things, but the important effects are these: the bytecode is stored in the `xemacs' executable binary, and all toplevel code has already been executed. If you (require 'foo) where foo is a package dumped with XEmacs, Nothing Happens as it has already been loaded. In order to get a more recent version, you have to explicitly (load "foo"). If you edit and rebytecompile the source lisp files in lisp/foo.el and lisp/foo.elc the changes won't be automatically reflected the next time you start XEmacs because nothing is being loaded at runtime. The term "autoload" refers to a definition of a Lisp symbol that doesn't really define the symbol, it tells the XEmacs binary where to load the Lisp bytecode that defines the symbol. In versions of XEmacs prior to 21.0, the autoloads were dumped with the binary, that is, they were static[1] from the time when the build was done. In 21.0, the autoloads are loaded at startup time. Consider this: An XEmacs 21.0 with $prefix pointing at /usr/local. This means that package searching will look into /usr/local/lib/xemacs/xemacs-packages for XEmacs packages. Install the Gnus package and then run `xemacs -vanilla' and C-h f gnus: gnus' is an interactive autoloaded Lisp function -- autoloads from "gnus" ... Kill this session, rm -rf lisp/gnus from the XEmacs packages and restart. Now C-h f gnus yields: [No match] and won't let you complete the prompt. The same exercise in XEmacs 20.4 will return the first result in both case because the autoloads are dumped with the XEmacs 20.4 binary. This *does not* mean that Gnus is dumped with the binary. It only means that Gnus symbols are recognized by the binary with instructions on where to load the lisp from if the symbols are evaluated. Are things clearer now? Correct. The first statement is irrelevant. XEmacs only loads the Lisp packages it is directed to, and it currently only loads a minimum of stuff in order to reach an Interactive Lisp buffer without loading anything else. They're not. In XEmacs 21, you will have the new package as if the first version of the package *never existed*. This is a huge win. I hope more folks can understand this. Using the correct meaning of "dumped a package with XEmacs", nothing will happen -- you have to redump XEmacs to get the updates and in XEmacs 20.4, you will have the new Lisp package, but autoloads from the previous version, so if a global function changes, it won't be reflected in how the user sees it. Footnotes: [1] The `autoload' function can be run manually, but it is more convenient to have them built automatically.