It's possible to customize Emacs in just about any way you can imagine. Almost everything you see on the screen, every command, keystroke, message, and so on, can be changed. As you may imagine, most customizations involve the Emacs startup file .emacs.
The previous section discussed the interactive customization tool, Custom, but left out some of the details on what happens any time you "save for future sessions." Custom places the configuration information in your .emacs file. Some things simply cannot be done through Custom (yet). Once you get familiar with the types of statements that go into your .emacs file, you may also just find it easier to add a line or two directly.
We should emphasize that using Custom or editing .emacs by hand is not an either-or proposition. When you save options via Custom, it adds its settings to the end of your .emacs file and warns you not to edit them by hand. Despite this prohibition, you can easily add your own customizations to the beginning of that file. To illustrate this, Example 10-1 shows a sample .emacs file for Mac OS X that shows edits made directly by the user as well as sections added by Custom (shown in bold)
Example 10-1. A .emacs file for Mac OS X with lines added by the user and by Custom
(setq mac-command-key-is-meta nil) (diary) (setq load-path (cons "~/elisp" load-path)) (autoload 'html-helper-mode "html-helper-mode" "Yay HTML" t) (setq html-helper-build-new-buffer t) (setq ...