1. Introduction to ESS

The S family (S, Splus and R) and SAS statistical analysis packages provide sophisticated statistical and graphical routines for manipulating data. Emacs Speaks Statistics (ESS) is based on the merger of two pre-cursors, S-mode and SAS-mode, which provided support for the S family and SAS respectively. Later on, Stata-mode was also incorporated.

ESS provides a common, generic, and useful interface, through emacs, to many statistical packages. It currently supports the S family, SAS, BUGS, Stata and XLisp-Stat with the level of support roughly in that order.

A bit of notation before we begin. emacs refers to both GNU Emacs by the Free Software Foundation, as well as XEmacs by the XEmacs Project. The emacs major mode ESS[language], where language can take values such as S, SAS, or XLS. The inferior process interface (the connection between emacs and the running process) referred to as inferior ESS (iESS), is denoted in the modeline by ESS[dialect], where dialect can take values such as S3, S4, S+3, S+4, S+5, S+6, S+7, R, XLS, VST, SAS.

Currently, the documentation contains many references to `S' where actually any supported (statistics) language is meant, i.e., `S' could also mean `XLisp-Stat' or `SAS'.

For exclusively interactive users of S, ESS provides a number of features to make life easier. There is an easy to use command history mechanism, including a quick prefix-search history. To reduce typing, command-line completion is provided for all S objects and "hot keys" are provided for common S function calls. Help files are easily accessible, and a paging mechanism is provided to view them. Finally, an incidental (but very useful) side-effect of ESS is that a transcript of your session is kept for later saving or editing.

No special knowledge of Emacs is necessary when using S interactively under ESS.

For those that use S in the typical edit--test--revise cycle when programming S functions, ESS provides for editing of S functions in Emacs edit buffers. Unlike the typical use of S where the editor is restarted every time an object is edited, ESS uses the current Emacs session for editing. In practical terms, this means that you can edit more than one function at once, and that the ESS process is still available for use while editing. Error checking is performed on functions loaded back into S, and a mechanism to jump directly to the error is provided. ESS also provides for maintaining text versions of your S functions in specified source directories.

1.1 Why should I use ESS?

Statistical packages are powerful software systems for manipulating and analyzing data, but their user interfaces often leave something something to be desired: they offer weak editor functionality and they differ among themselves so markedly that you have to re-learn how to do those things for each package. ESS is a package which is designed to make editing and interacting with statistical packages more uniform, user-friendly and give you the power of emacs as well.

ESS provides several features which make it easier to interact with the ESS process (a connection between your buffer and the statistical package which is waiting for you to input commands). These include:

• Command-line editing for fixing mistakes in commands before they are entered. The `-e' flag for S-plus provides something similar to this, but here you have the full range of Emacs commands rather than a limited subset. However, other packages such as XLisp-Stat and S3 do not necessarily have features like this built-in. See section 4.1 Entering commands and fixing mistakes.

• Searchable command history for recalling previously-submitted commands. This provides all the features of the `Splus -e' history mechanism, plus added features such as history searching. See section 4.5 Command History.

• Command-line completion of both object and file names for quick entry. This is similar to tcsh's facility for filenames; here it also applies to object names and list components. See section 4.2 Completion of object names.

• Hot-keys for quick entry of commonly-used commands in `S' such as objects() and search(). See section 4.7 Hot keys for common commands.

• Transcript recording for a complete record of all the actions in an S session. See section 4.4 Manipulating the transcript.

• Interface to the help system, with a specialized mode for viewing S help files. See section 9. Reading help files.

If you commonly create or modify S functions, you will have found the standard facilities for this (the `fix()' function, for example) severely limiting. Using S's standard features, one can only edit one function at a time, and you can't continue to use S while editing. ESS corrects these problems by introducing the following features:

• Object editing. ESS allows you to edit more than one function simultaneously in dedicated Emacs buffers. The ESS process may continue to be used while functions are being edited. See section 7.1 Creating or modifying S objects.

• A specialized editing mode for S code, which provides syntactic indentation and highlighting. See section 7.5 Indenting and formatting S code.

• Facilities for loading and error-checking source files, including a keystroke to jump straight to the position of an error in a source file. See section 7.3 Detecting errors in source files.

• Source code revision maintenance, which allows you to keep historic versions of S source files. See section 7.7 Maintaining S source files.

• Facilities for evaluating S code such as portions of source files, or line-by-line evaluation of files (useful for debugging). See section 7.4 Sending code to the ESS process.

Finally, ESS provides features for re-submitting commands from saved transcript files, including:

• Evaluation of previously entered commands, stripping away unnecessary prompts. See section 4.4.3 Re-submitting commands from the transcript.

1.2 New features in ESS

Changes/New Features in 5.2.7:

• If you use Custom to change the variable ess-toolbar-items, the new toolbar is used in all subsequent ESS buffers.
• ESS[SAS]: new feature: if ess-sas-log-max >0 and your .log grows to more than ess-sas-log-max bytes, just the first ess-sas-log-max bytes are refreshed; this is helpful when your .sas program generates lots of error messages and gets too big for emacs to display
• ESS[R/S]: M-; in R/S editing modes will now indent with either one or two hashes depending on context.
• ESS[R]: David Whiting's Sweave extensions (to 'noweb') are now available (from ess-swv.el loaded by default).

Changes/New Features in 5.2.6:

• Removed non-ASCII characters in a few files.
• ESS[R]: now works better when UTF-8 locale is active; in particular, you get correct directional quotes in R's startup message for R-devel (unstable development version of R 2.1.0) when using environment variables LANGUAGE=en@quot LC_ALL=en_US.UTF-8
• ESS[SAS]: toggling of .log mode improved (F10); toggling of .lst mode now also available (C-F10); killing all buffers associated with .sas program no longer bound to C-F10 since its a bit overzealous; EXPERIMENTAL new feature: if your .log grows to more than 2.5MB, just the first 2.5MB are refreshed; this is helpful when your .sas program generates lots of error messages and gets too big for emacs to display; the truncation size is controlled by the variable ess-sas-log-max and defaults to 2500000.
• S-Plus 7 for Windows is now recognized.
• ESS[S] (incl. R): in auto-fill mode, strings are not wrapped anymore.
• ESS[S] (incl. R): font-lock now correctly differs between R and S, e.g., for "_"; both now fontify warning(.) and S does terminate() additionally.
• Support for `bell' aka `beep' aka `ding' aka `alarm' in all inferior modes: When \a is output "to the the console" at the beginning of a line, the bell is rung.

Changes/New Features in 5.2.5:

• ESS[R]: C-c C-q or `Quit S' from the menu now should work (again and less klunkily) and do not append `-exited' to the buffer name. Further, the behavior of (ess-cleanup), called from ess-quit, now depends on the new customizable variable ess-S-quit-kill-buffers-p which defaults to nil. Consequently, the question "Delete all buffers associated with ..?" will not be asked anymore by default.
• ESS[SAS] -- ess-ebcdic-to-ascii-search-and-replace will now work with the recode application as well which is available on many platforms
• ESS[S] (incl. R): Name completion for slots of S4 objects now works!

Changes/New Features in 5.2.4:

• The documentation now includes an overview of how to use the emacs TAGS facility for S functions. (The distribution also used to contain a directory `etc/other/Tags' where a ~1990 version of `etags.c' was distributed; this is no longer relevant and so has been deleted.)
• ESS[SAS] -- When you are working with EBCDIC files on an ASCII platform, .log NOTEs may display as gibberish since the EBCDIC characters are not converted to ASCII prior to their display. So, the function ess-ebcdic-to-ascii-search-and-replace is provided for convenience and is bound to C-F11. This function requires the dd command (only available on unix or unix-like platforms).
• ESS: Completion of object names is now always done dynamically rather than allowing the option of using a pre-computed database (by ess-create-object-name-db) since modern computers seem fast enough for dynamic completion. (We expect few users, if any, have been using the pre-computed database method.)
• ESS: object completion in iESS buffers running on Windows was very slow (for GNU Emacs, but not XEmacs) and has now been fixed. Further, it was more or less broken for all versions of S-plus 6.x, and has been fixed to work everywhere but with the Windows' GUI of S-plus. The list of objects now shows unique names also when an object appears more than once in the search path.
• ESS[R]: Completion of object names now also includes those starting with ".".

Changes/New Features in 5.2.3:

• ESS: When new inferior ESS processes are created, by default they will replace the current buffer (this restores behavior from pre 5.2.0). If you wish new ESS processes to start in another window of the current frame, set inferior-ess-same-window to nil.
• New variables inferior-Splus-args and inferior-R-args provide a way to pass command line arguments to starting S and R processes.

Changes/New Features in 5.2.2:

• bug-fixes for 5.2.1 (require 'executable), html docs, etc.
• ess-lisp-directory/../doc/info added to Info-directory-list if ess-info not found by info
• ESS[R]: If you have other versions of R on your exec-path, such as "R-1.8.1" with Unix or "rw1081" with Windows, ESS will find them and create appropriate functions, such as M-x R-1.8.1 or M-x rw1081, for calling them. By default only Unix programs beginning "R-1" and "R-2" and Windows programs parallel to the version of R in your exec-path will be found, but see ess-r-versions and ess-rterm-versions for ways to find other versions of R.
• ESS[R]: Other versions of R, such as "R-1.8.1" on Unix and "rw1081" on Windows, are added to the "ESS / Start Process / Other" menu.
• ESS[S]: If you have other versions of S-Plus on your Windows computer, such as S-Plus 6.1 or S-Plus 4.5, ESS will find them and create appropriate functions, such as M-x splus61, for calling the console version (Sqpe) inside an emacs buffer. By default only programs installed in the default location will be found, but see ess-SHOME-versions for ways to find other versions of S-Plus.
• ESS[S]: Other versions of Sqpe on Windows, such as "splus61", are added to the "ESS / Start Process / Other" menu.
• ESS[R]: (bug fix) ess-quit (bound to C-c C-q) should now quit the inferior R process, when issued from either the inferior buffer, or from a .R buffer.

Changes/New Features in 5.2.1:

• ESS[S] (R and S-plus): now have toolbar support with icons to evaluate code in the inferior process or to switch there. This code is experimental and likely to change as XEmacs/Emacs issues get resolved. The toolbar should be enabled if your Emacs displays images, but can be disabled with the variable ess-use-toolbar. Thanks to David Smith from Insightful for the S-plus logo.
• ESS[SAS]: ess-sas-graph-view (F12) enhanced; you can specify external file viewers for each graphics file type via the alist ess-sas-graph-view-viewer-alist; also .jpg/.gif are now handled by image-mode on XEmacs, if available, otherwise by graphics primitives as before

Changes/New Features in 5.2.0:

• ESS[BUGS]: new info documentation! now supports interactive processing thanks to Aki Vehtari; new architecture-independent unix support as well as support for BUGS v. 0.5
• ESS[SAS]: convert .log to .sas with ess-sas-transcript; info documentation improved; Local Variable bug fixes; SAS/IML statements/functions now highlighted; files edited remotely by ange-ftp/EFS/tramp are recognized and pressing SUBMIT opens a buffer on the remote host via the local variable ess-sas-shell-buffer-remote-init which defaults to "ssh"; changed the definition of the variable ess-sas-edit-keys-toggle to boolean rather than 0/1; added the function ess-electric-run-semicolon which automatically reverse indents lines containing only "run;"; C-F1 creates MS RTF portrait from the current buffer; C-F2 creates MS RTF landscape from the current buffer; C-F9 opens a SAS DATASET with PROC INSIGHT rather than PROC FSVIEW; "inferior" aliases for SAS batch: C-c C-r for submit region, C-c C-b for submit buffer, C-c C-x for goto .log; C-c C-y for goto .lst
• ESS[S]: Pressing underscore ("_") once inserts " <- " (as before); pressing underscore twice inserts a literal underscore. To stop this smart behaviour, add "(ess-smart-underscore nil)" to your .emacs after ess-site has been loaded; ess-dump-filename-template-proto (new name!) now can be customized successfully (for S language dialects); Support for Imenu has been improved; set ess-imenu-use-S to non-nil to get an "Imenu-S" item on your menubar; ess-help: Now using nice underlines (instead of `nuke-* ^H_')
• ESS[R]: After (require 'essa-r), M-x ess-r-var allows to load numbers from any Emacs buffer into an existing *R* process; M-x ess-rdired gives a "directory editor" of R objects; fixed ess-retr-lastvalue-command, i.e. .Last.value bug (thanks to David Brahm)
• ESS: Support for creating new window frames has been added to ESS. Inferior ESS processes can be created in dedicated frames by setting inferior-ess-own-frame to t. ESS help buffers can also open in new frames; see the documentation for ess-help-own-frame for details. (Thanks to Kevin Rodgers for contributing code.)

Changes/New Features in 5.1.24:

• The version number is now correct even inside ESS/Emacs

Changes/New Features in 5.1.23:

• Minor more Makefile clean up.

Changes/New Features in 5.1.22:

• Besides info documentation, PDF and HTML documentation are also provided (instead of built using "make") and available on the web as well; see ESS web page and StatLib
• Now that info documentation is available, the README.* files are no longer supported. However, they are still distributed for what it's worth.
• ESS is now an XEmacs package! See XEmacs Installation HOWTO for details (specifically, items 10-15).
• ESS[SAS]: more user-friendly enhancements for remote SAS batch jobs with Kermit file transfers (LOG and OUTPUT function key features now supported). Multiple shells now supported so you can run SAS on different computers from different buffers by setting the buffer-local variable ess-sas-shell-buffer to unique buffer names.
• Major re-vamping of Makefile/Makeconf.

Changes/New Features in 5.1.21:

• ESS[SAS]: info documentation now available!, see ESS->Help for SAS; F12 opens GSASFILE nearest point for viewing either within emacs, when available, or via an external viewer; more syntax highlighting keywords; more enhancements for remote SAS batch jobs with Kermit; new framework for remote SAS interactive jobs, see ess-remote
• ESS[S]: info documentation now available!, see ESS->Help for the S family
• Makefile: tag now independent of rel; info files made by doc/Makefile and installed in new info sub-directory

Changes/New Features in 5.1.20:

• New `options()$STERM' in the S dialects (S, S-Plus, R). The S program can determine the environment in which it is currently running. ESS sets the option to `iESS' or `ddeESS' when it starts an S language process. We recommend other specific values for S language processes that ESS does not start.
• New `ess-mouse-me' function, assigned to S-mouse-3 by default. User may click on a word or region and then choose from the menu to display the item, or a summary, or a plot, etc. This feature is still under development.
• GNU Emacs 21.1 is now supported (fixed for S dialects, SAS & BUGS), (some from Stephen Eglen).
• XEmacs 21.x is now supported (fixed w32-using-nt bug)
• XEmacs on Win (NT) is better supported.
• Workaround for bug in Sqpe+6 (S-PLUS 6 for Win).
• should now work even when imenu is not available (for old XEmacsen).
• ESS[SAS]: XEmacs-Imenu fix; C-TAB is globalized along with your function-key definitions, if specified; you can specify your SAS library definitions outside of autoexec.sas for ess-sas-data-view with SAS code placed in the variable ess-sas-data-view-libname, also the dataset name is defaulted to the nearest permanent dataset to point; Speedbar support now works for permanent datasets, please ignore first./last.; new font-locking is now the default with more improvements for font-locking PROCs, macro statements, * ; and %* ; comments; you can toggle sas-log-mode with F10 which will font-lock your .log (if it isn't too big); submit remote .sas files accessed with ange-ftp, EFS or Tramp (Kermit is experimental) by setting ess-sas-submit-method to 'sh; ess-sas-submit-command and ess-sas-submit-command-options are buffer-local so you can have local file variable sections at the end of your .sas files to request different executables or specify special options and the local file variables are re-read at submit instead of only at file open so that if you make a change it is picked up immediately;
• ESS[BUGS]: font-lock with `in' fixed.
• for STATA: font-lock bug fixed.
• for Rd mode: C-c C-v and `switch-process' in menu. further, C-c C-f prefix (Rd-font) for inserting or surrounding a word by things such as \code{.}, \code{\link{.}}, \emph{.} etc.
• new functions (ess-directory-function) and (ess-narrow-to-defun) ess-directory <-> default-directory logic (Jeff Mincy).
• Re-organized Makefile and fixed a few bugs.

Changes/New Features in 5.1.19:

• S+6 now supported (Tony Rossini (Unix) and Rich Heiberger (Windows))
• New BUGS support through ESS[BUGS] mode (Rodney Sparapani) Templates assist you in writing .bug and .cmd code (.cmd and .log are replaced by .bmd and .bog to avoid emacs extension collisions). Substitution" parameters facilitate "automagic" generation of data...in" and "init...in" filenames, "const N=" from your data file and "monitor()/stats()" commands. Activated by pressing F12.
• Fixes for `ess-smart-underscore' SAS breakage (Rich Heiberger)
• You can change between PC and Unix, local and global SAS function-key definitions interactively (Rich Heiberger)
• C-Submit a highlighted region to SAS batch (Rodney Sparapani)
• New and improved SAS syntax highlighting (Rodney Sparapani) To get the new functionality, set ess-sas-run-make-regexp to nil. Also available in .log files via F10.
• Open a permanent SAS dataset for viewing via F9 (Rodney Sparapani) You must have the library defined in autoexec.sas for it to work.
• User-friendly defaults for `sas-program', `ess-sas-batch-pre-command' and `ess-sas-batch-post-command' as well Customize support for these and other ESS[SAS] variables (Rodney Sparapani)
• `ess-sas-suffix-2' now defaults to .dat via F11 (Rodney Sparapani)
• Emacs/XEmacs, Unix/Windows issues collectively handled in ess-emcs.el
• defadvice solves problem of missing *ESS* (thanks to Jeff Mincy)
• Improved manual a bit by including things that were only in `README'.

Changes/New Features in 5.1.18:

• New `ess-smart-underscore' function, now assigned to "_" by default. Inserts `ess-S-assign' (customizable " <- "), unless inside string and comments where plain "_" is used instead. (MM)
• Fixes for longstanding interactive SAS breakage (RMH)

Changes/New Features in 5.1.17:

• Documentation for Windows Installation (Rich Heiberger)
• removal of ess-vars, finalization of customize support (in the sense that there is no more use of ess-vars, but that we need to fix ess-cust) (AJ Rossini)
• Many small (and large) fixes/contributions (MMaechler)
• addition of the "S-equal" variable and provide M-x ess-add-MM-keys a way to remap "_" to `ess-S-assign', typically " <- ", but customizable. (MMaechler)

Changes/New Features in 5.1.16:

• BUG FIXES
• Better SAS support

Changes/New Features in 5.1.15:

• BUG FIXES

Changes/New Features in 5.1.14:

• Yet more fixes to SAS mode, (Rich Heiberger and Rodney Sparapani)
• Customize support (for most Emacsen which support it) (AJRossini)
• ARC and ViSta support out of the box, and fixes for XLispStat (AJRossini)

Changes/New Features in 5.1.13:

• Version numbering finally all depending on the ./VERSION file, thanks to Martin Maechler.
• Yet more fixes to SAS mode, thanks to Rich Heiberger.

Changes/New Features in 5.1.12:

• Splus 5.1 stabilized, thanks to Martin Maechler, Bill Venables, Chuck Taylor, and others.
• More fixes to SAS mode, thanks to Rodney Sparapani and Rich Heiberger.

Changes/New Features in 5.1.11:

• More fixes to Stata mode, thanks to Brendan Halpin.
• fixed bugs in ESS-elsewhere, thanks to many testers
• README.SPLUS4WIN has DETAILED instructions for S-PLUS 2000, thanks to David Brahm.
• Fixes to SAS mode, thanks to Rodney Sparapani

Changes/New Features in 5.1.10:

• More fixes to Stata mode
• primitive generic version of ESS-elsewhere
• Small fixes to SAS/Stata.

Changes/New Features in 5.1.9:

• Stata mode works
• Literate Data Analysis using Noweb works

Changes/New Features in 5.1.8:

• Bug fixes
• R documentation mode defaults changed

Changes/New Features in 5.1.2:

• able to use inferior iESS mode to communicate directly with a running S-Plus 4.x process using the Microsoft DDE protocol. We use the familiar (from Unix ESS) C-c C-n and related key sequences to send lines from the S-mode file to the inferior S process. We continue to edit S input files in ESS[S] mode and transcripts of previous S sessions in ESS Transcript mode. All three modes know the S language, syntax, and indentation patterns and provide the syntactic highlighting that eases the programming tasks.

1.3 Authors of and contributors to ESS

The ESS environment is built on the open-source projects of many contributors, dating back nearly 15 years. Doug Bates and Ed Kademan wrote S-mode in 1989 to edit S and Splus files in GNU Emacs. Frank Ritter and Mike Meyer added features, creating version 2. Meyer and David Smith made further contributions, creating version 3. For version 4, David Smith provided process interaction based on Olin Shivers' comint package.

John Sall wrote GNU Emacs macros for SAS source code around 1990. Tom Cook added more functionality creating SAS-mode which was distributed in 1994. Also in 1994, A.J. Rossini extended S-mode to support XEmacs. Together with extensions written by Martin Maechler, this became version 4.7 and supported S, Splus, and R. In 1995, Rossini extended SAS-mode to work with XEmacs.

In 1997, Rossini merged S-mode and SAS-mode into a single Emacs package for statistical programming; the product of this marriage was called ESS version 5.

• The multiple process code, and the idea for ess-eval-line-and-next-line are by Rod Ball.

• Thanks to Doug Bates for many useful suggestions.

• Thanks to Martin Maechler for reporting and fixing bugs, providing many useful comments and suggestions, and for maintaining the S-mode mailing list.

• Thanks to Frank Ritter for updates from the previous version, the menu code, and invaluable comments on the manual.

• Thanks to Ken'ichi Shibayama for his excellent indenting code, and many comments and suggestions.

• Last but definitely not least, thanks to the many beta testers of the S-mode and ESS mailing lists.

ESS version 5 is being developed and currently maintained by

• A.J. Rossini
• Richard M. Heiberger
• Kurt Hornik
• Martin Maechler
• Rodney A. Sparapani
• Stephen Eglen

1.4 Getting the latest version of ESS

The latest released version of ESS is always available on the web at: ESS web page or StatLib

The latest development version of ESS is available via https://svn.R-project.org/ESS/, the ESS Subversion repository. If you have a Subversion client (see http://subversion.tigris.org/), you can download the sources using:

% svn checkout https://svn.r-project.org/ESS/trunk path

If you remove other versions of ESS from your emacs load-path, you can then use the development version by adding the following to .emacs:

(load "/path/to/ess-svn/lisp/ess-site.el") 

Note that https is required, and that the SSL certificate for the Subversion server of the R project is

Certificate information:
 - Hostname: svn.r-project.org
 - Valid: from Jul 16 08:10:01 2004 GMT until Jul 14 08:10:01 2014 GMT
 - Issuer: Department of Mathematics, ETH Zurich, Zurich, Switzerland, CH
 - Fingerprint: c9:5d:eb:f9:f2:56:d1:04:ba:44:61:f8:64:6b:d9:33:3f:93:6e:ad

(currently, there is no "trusted certificate"). You can accept this certificate permanently and will not be asked about it anymore.

1.5 How to read this manual

If you need to install ESS, read 2. Installing ESS on your system for details on what needs to be done before proceeding to the next chapter.

In this manual we use the standard notation for describing the keystrokes used to invoke certain commands. C-<chr> means hold the CONTROL key while typing the character <chr>. M-<chr> means hold the META or EDIT or ALT key down while typing <chr>. If there is no META, EDIT or ALT key, instead press and release the ESC key and then type <chr>.

All ESS commands can be invoked by typing M-x command. Most of the useful commands are bound to keystrokes for ease of use. Also, the most popular commands are also available through the emacs menubar, and finally, if available, a small subset are provided on the toolbar. Where possible, keybindings are similar to other modes in emacs to strive for a consistent user interface within emacs, regardless of the details of which programming language is being edited, or process being run.

Some commands, such as M-x R can accept an optional `prefix' argument. To specify the prefix argument, you would type C-u before giving the command. e.g. If you type C-u M-x R, you will be asked for command line options that you wish to invoke the R process with.

Emacs is often referred to as a `self-documenting' text editor. This applies to ESS in two ways. First, limited documentation about each ESS command can be obtained by typing C-h f. For example, if you type C-h f ess-eval-region, documentation for that command will appear in a separate *Help* buffer. Second, a complete list of keybindings that are available in each ESS mode and brief description of that mode is available by typing C-h m within an ESS buffer.

Emacs is a versatile editor written in both C and lisp; ESS is written in the Emacs lisp dialect (termed `elisp') and thus benefits from the flexible nature of lisp. In particular, many aspects of ESS behaviour can be changed by suitable customization of lisp variables. This manual mentions some of the most frequent variables. A full list of them however is available by using the Custom facility within emacs. (Type M-x customize-group RET ess RET to get started.) A. Customizing ESS provides details of common user variables you can change to customize ESS to your taste, but it is recommended that you defer this section until you are more familiar with ESS.